Patient-side occlusion detection system for a medication infusion system

ABSTRACT

A system for detecting an occlusion in a fluid line is disclosed which can detect occlusions in the downstream or patient side of a disposable cassette containing a fluid pump thereon. The cassette includes a pressure diaphragm and is for installation onto and use with a main pump unit including a pressure transducer therein for monitoring fluid pressure downstream of the pump. The system utilizes control circuitry to provide an alarm in the event of a patient-side occlusion, and the occlusion detection system works when the system is configured as any of a number of difference device types, including both a flow controller emulation and several different infusion pump configurations.

IDENTIFICATION OF RELATED PATENT APPLICATIONS

This application is related to seven other copending patentapplications, all of which were filed on Dec. 1, 1987. These patentapplications are U.S. Ser. No. 127,333, entitled "Disposable Cassettefor a Medication Infusion System," U.S. Ser. No. 127,350, entitled"Piston Cap and Boot Seal for a Medication Infusion System," U.S. Ser.No. 128,122, entitled "Pressure Diaphragm for a Medication InfusionSystem," U.S. Ser. No. 128,009, entitled "Cassette OpticalIdentification Apparatus for a Medication Infusion System," U.S. Ser.No. 128,121, entitled "Air-In-Line Detector for a Medication InfusionSystem," U.S. Ser. No. 127,359, entitled "Cassette Loading and LatchingApparatus for a Medication Infusion System," and U.S. Ser. No. 127,133,entitled "Mechanical Drive System for a Medication Infusion System."

This application is also related to three other concurrently filedcopending patent applications. These patent applications are U.S. Ser.No. 128,973, entitled "Fluid Delivery Control and Monitoring Apparatusfor a Medication Infusion System," U.S. Ser. No. 128,966, entitled"Clinical Configuration of Multimode Medication Infusion System," andU.S. Ser. No. 128,978, entitled "User Interface for Medication InfusionSystem."

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates generally to a system for detecting anocclusion in a fluid line, and more particularly to a system fordetecting occlusions in the downstream or patient side of a disposablecassette containing a fluid pump thereon, which disposable cassetteincludes a pressure diaphragm and is for installation onto and use witha main pump unit including a pressure transducer therein for monitoringfluid pressure downstream of the pump, the system utilizing controlcircuitry to provide an alarm in the event of a patient-side occlusion.

In the past there have been two primary techniques which have been usedto deliver drugs which may not be orally ingested to a patient. Thefirst such technique is through an injection, or shot, using a syringeand needle which delivers a large dosage at relatively infrequentintervals to the patient. This technique is not always satisfactory,particularly when the drug being administered is potentially lethal, hasnegative side effects when delivered in a large dosage, or must bedelivered more or less continuously to achieve the desired therapeuticeffect. This problem results in smaller injections being given at morefrequent intervals, a compromise approach not yielding satisfactoryresults.

Alternatively, the second technique involves administering a continuousflow of medication to the patient, typically through an IV bottle.Medication may also be delivered through an IV system with an injectionbeing made into a complex maze of IV tubes, hoses, and otherparaphernalia. With drop counters being used to meter the amount of bulkfluid delivered, many medications still end up being administered in alarge dosage through an injection into the IV lines, although themedications may be diluted somewhat by the bulk fluid.

As an alternative to these two techniques of administering medication toa patient, the relatively recent addition of medication infusion pumpshas come as a welcome improvement. Medication infusion pumps areutilized to administer drugs to a patient in small, metered doses atfrequent intervals or, alternatively, in the case of some devices, at alow but essentially continuous rate. Infusion pump therapy may beelectronically controlled to deliver precise, metered doses at exactlydetermined intervals, thereby providing a beneficial gradual infusion ofmedication to the patient. In this manner, the infusion pump is able tomimic the natural process whereby chemical balances are maintained moreprecisely by operating on a continuous time basis.

One of the requirements of a medication infusion system is dictated bythe important design consideration of disposability. Since the portionof the device through which medication is pumped must be sterile, inmost applications of modern medication infusion equipment some portionsof the equipment are used only once and then disposed of, typically atregular intervals such as once daily. It is therefore desirable that thefluid pump portion of the infusion pump device be disposable, with thefluid pump being designed as an attachable cassette which is ofinexpensive design, and which is easily installable onto the main pumpunit.

It will be perceived that it is desirable to have a simple disposablecassette design to minimize the cost of construction of the cassette,using the minimum number of parts necessary in the design of thecassette. The design of the cassette must be mass producible, and yetresult in a uniform cassette which is capable of delivering liquidmedication or other therapeutic fluids with a high degree of accuracy.The cassette should include therein more than just a fluid pump; otherfeatures which have formerly been included in peripheral devices may beincluded in the cassette.

It is the primary objective of the present invention to provide an alarmin the event of an occlusion in the fluid path downstream of the pump inthe disposable cassette. The occlusion detection system must beintegrally contained in the disposable cassette/main pump unitcombination, and not an add-on downstream type. An patient-sideocclusion detector must provide a number of advantages and meet a numberof requirements necessary to enhance operating safety of the overallsystem. Specifically, the patient-side occlusion detection system of thepresent invention must respond quickly to "rapid occlusions" such asthose caused by a clamped line or a closed stopcock. Rapid response isrequires to prevent fluid pressure from quickly exceeding a maximumvalue.

The patient-side occlusion detection system of the present inventionmust minimize the occurrence of nuisance alarms during false "slowocclusions" such as those caused by transient fluctuations such asvascular pressure, head height, or motion of the patient, which are notin fact occlusions at all. The system must however provide an alarm inthe event of true "slow occlusions" which may be caused by pressureslowly increasing to a high level due to a clotted or infiltrated fluidline. The system of the present invention must also provide flexibilityin the maximum pressure generated without causing an alarm, since someinfusates require more pressure to infuse than others.

Perhaps most important is the ability of a patient-side occlusiondetection system to provide an alarm in a minimal time from the onset ofan occlusion. That is to say that the system of the present inventionmust afford a high degree of precision and accuracy which must remainconstant throughout the life of the cassette, and it must not besignificantly affected by other operating components of the system. Inaddition, the occlusion detection system of the present invention mustalso require low power to operate, to therefore conserve power andextend battery life.

The occlusion detection system of the present invention must be of adesign which enables it to compete economically with known competingsystems. It must accomplish all these objects in a manner which willretain all of the advantages of ease of use, reliability, durability,and safety of operation, without incurring any relative disadvantage.All the advantages of the present invention will result in a superiormedication infusion system having a number of advantages making thesystem a highly desirable alternative to systems presently available.

SUMMARY OF THE INVENTION

The disadvantages and limitations of the background art discussed aboveare overcome by the present invention. With this invention, a disposablecassette having only seven components therein is described. The cassetteutilizes a highly accurate and reliable piston-type fluid pump and anactive valve design of unparalleled accuracy, simplicity, and accuracyof operation. A bubble trap is included in the cassette for removing airbubbles introduced into the system, and a bubble detector is used toensure that fluid supplied to a patient is virtually bubble-free. Thesystem is designed to operate as a number of different pumps, such as ageneral purpose infusion pump, a neonatal infusion pump, a home healthcare infusion pump, an operating room pump, a patient-controlledanalgesia (PCA) pump, or to emulate the operation of a flow controller(the traditional bottle and gravity flow type of system). For thepurposes of the present invention, the occlusion detection systemdiscriminates only between operation as a flow controller and operationas any of the other device types.

The disposable cassette for use with the system of the present inventionincludes a pressure diaphragm for enabling pressure sensing of theoutlet line. The pressure diaphragm is integrated into the design of thecassette, and includes a circular raised pressure plateau on thecassette housing. The fluid channel on the outlet side of the fluid pumpin the cassette leads to one side of the pressure plateau, and a fluidoutlet leads from the other side of the pressure plateau.

A thin elastomeric diaphragm disposed over the top of the housingincludes a raised cylindrical portion including the pressure diaphragmon the top thereof which fits around and over the pressure plateau. Thefluid path is between the top of the pressure plateau and the pressurediaphragm, between the sides of the pressure plateau and the cylindricalportion of the diaphragm, and through a channel located in the surfaceof the pressure plateau between the fluid inlet and the fluid outlet.

The pressure diaphragm is accordingly free to move to transmit the fluidpressure thereunder, unlike most previously known designs. When thecassette is installed onto a main pump unit, the pressure diaphragm willbear against a pressure transducer mounted in the main pump unit. Fluidpressure within the cassette on the outlet side or patient side of thepump will thusly be transmitted by the pressure diaphragm to thepressure transducer, which will provide an output indicative of thefluid pressure.

The output of the pressure transducer is amplified, filtered, andconverted to a digital pressure signal. The first difference of thepressure signal is also obtained for an indication of pressure changerate. For rapid pressure change rates, the present invention uses aone-step ahead predictor to ensure that pressure does not exceed themaximum limit of the system, with an alarm being sounded when the outputof the one-step ahead predictor reaches the alarm threshold. The systemis designed to operate as described above with the alarm thresholdeither for flow controller emulation, or with a higher alarm thresholdfor all other device types.

For slower pressure change rates, the system operates in two discretefashions depending on whether the system is configured to emulate a flowcontroller or as any one of the other device types. For operation as aflow controller with slower pressure change rates, the pressure signalis digitally filtered, and monitored to ensure it does not exceed anabsolute maximum value. If it exceeds this absolute maximum value, thealarm is sounded.

For operation as any device type other than a flow controller, thesystem uses a baseline approach to respond to slower pressure changes. Abaseline pressure is calculated after infusion begins, and againwhenever the infusion rate is changed. Depending on which one of thedevice types other than a flow controller is being used, a specificincrement amount above the baseline pressure is the baseline alarmthreshold at which pressure an alarm is sounded. In addition, the systemalso has a built-in absolute maximum pressure of fifteen PSI, abovewhich the alarm will be sounded.

The patient-side occlusion detection system of the present inventionthereby provides an alarm in the event of an occlusion in the fluid pathdownstream of the pump in the disposable cassette. The occlusiondetection system is integrally contained in the disposable cassette/mainpump unit combination, and is not an add-on downstream type. Thepatient-side occlusion detector provides a number of advantages andmeets the above requirements necessary to enhance the operating safetyof the overall system. The patient-side occlusion detection system ofthe present invention responds quickly to "rapid occlusions" such asthose caused by a clamped line or a closed stopcock to prevent fluidpressure from quickly exceeding a maximum value.

The patient-side occlusion detection system of the present inventionminimizes the occurrence of nuisance alarms during false "slowocclusions" such as those caused by transient fluctuations such aschanges in intravascular pressure or head height, and motion of thepatient. The system does provide an alarm in the event of true "slowocclusions" which are caused by pressure slowly increasing to a highlevel due to a clotted or infiltrated fluid line. The system of thepresent invention also provides flexibility in the maximum pressuregenerated without causing an alarm, and is specifically designed to workwith a number of different pump configurations.

The patient-side occlusion detection system of the present inventionprovides an alarm in a minimal time from the onset of an occlusion. Itaffords a high degree of precision and accuracy which remain constantthroughout the life of the cassette, and it is not be significantlyaffected by other operating components of the system. It also requireslow power to operate, therefore conserving power and extending batterylife. The occlusion detection system of the present invention is of adesign which enables it to compete economically with known competingsystems. It accomplishes all the above objects in a manner which retainsall of the advantages of ease of use, reliability, durability, andsafety of operation, without incurring any relative disadvantage. Theadvantages of the present invention result in a superior medicationinfusion system having a number of advantages making the system a highlydesirable alternative to systems presently available.

DESCRIPTION OF THE DRAWINGS

In the detailed description of the preferred embodiment a uniformdirectional system is used in which front, back, top, bottom, left, andright are indicated with respect to the operating position of thecassette and main pump unit when viewed from the front of the main pumpunit. These and other advantages of the present invention are bestunderstood with reference to the drawings, in which :

FIG. 1 is a top plan view of a disposable cassette body showing most ofthe fluid path through the cassette;

FIG. 2 is a front side view of the cassette body shown in FIG. 1;

FIG. 3 is a back side view of the cassette body shown in FIGS. 1 and 2;

FIG. 4 is a bottom view of the cassette body shown in FIGS. 1 through 3;

FIG. 5 is a right side view of the cassette body shown in FIGS. 1through 4;

FIG. 6 is a left side view of the cassette body shown in FIGS. 1 through5;

FIG. 7 is a partially cutaway view from the front side of the cassettebody shown in FIGS. 1 through 6, showing the bubble trap used to removeair bubbles from the fluid supplied to the cassette;

FIG. 8 is a partially cutaway view from the right side of the cassettebody shown in FIGS. 1 through 6, showing the cylinder of the fluid pumpcontained in the cassette;

FIG. 9 is a top plan view of a valve diaphragm used to seal thepassageways on the top surface of the cassette body shown in FIG. 1, tofunction as the pressure diaphragm, and also to function as the valvesfor the pump;

FIG. 10 is a bottom view of the valve diaphragm shown in FIG. 9;

FIG. 11 is a cutaway view from the back side of the valve diaphragmshown in FIGS. 9 and 10;

FIG. 12 is a cutaway view from the right side of the valve diaphragmshown in FIGS. 9 and 10;

FIG. 13 is a top plan view of a valve diaphragm retainer used to retainthe valve diaphragm shown in FIGS. 9 through 12;

FIG. 14 is a bottom view of the valve diaphragm retainer shown in FIG.13;

FIG. 15 is a back side view of the valve diaphragm retainer shown inFIGS. 13 and 14;

FIG. 16 is a front side view of the valve diaphragm retainer shown inFIGS. 13 through 15;

FIG. 17 is a right side view of the valve diaphragm retainer shown inFIGS. 13 through 16;

FIG. 18 is a left side view of the valve diaphragm retainer shown inFIGS. 13 through 17;

FIG. 19 is a cutaway view from the front side of the valve diaphragmretainer shown in FIGS. 13 through 18;

FIG. 20 is a cutaway view from the left side of the valve diaphragmretainer shown in FIGS. 13 through 19;

FIG. 21 is a cutaway view from the right side of the valve diaphragmretainer shown in FIGS. 13 through 20;

FIG. 22 is a top view of a bubble chamber cap;

FIG. 23 is a bottom view of the bubble chamber cap shown in FIG. 22;

FIG. 24 is a left side view of the bubble chamber cap shown in FIGS. 22and 23;

FIG. 25 is a cutaway view from the back side of the bubble chamber capshown in FIGS. 22 through 24;

FIG. 26 is a cutaway view from the right side of the bubble chamber capshown in FIGS. 22 through 24;

FIG. 27 is a top plan view of a slide latch used both to lock thecassette in place on a main pump unit, and to pinch off the IV outletline prior to installation on the main pump unit;

FIG. 28 is a right side view of the slide latch shown in FIG. 27;

FIG. 29 is a bottom view of the slide latch shown in FIGS. 27 and 28;

FIG. 30 is a back side view of the slide latch shown in FIGS. 27 through29;

FIG. 31 is a front side view of the slide latch shown in FIGS. 27through 30;

FIG. 32 is a cutaway view from the left side of the slide latch shown inFIGS. 27 through 31;

FIG. 33 is a side plan view of the piston cap and boot seal, whichfunction both as a piston and as a bacterial seal;

FIG. 34 is a top end view of the piston cap and boot seal shown in FIG.33; FIG. 35 is a bottom end view of the piston cap and boot seal shownin FIGS. 33 and 34; FIG. 36 is a cutaway view from the side of thepiston cap and boot seal shown in FIGS. 33 through 35; FIG. 37 is a backside plan view of a piston for insertion into the piston cap and bootseal shown in FIGS. 33 through 36; FIG. 38 is a front side view of thepiston shown in FIG. 37; FIG. 39 is a top view of the piston shown inFIGS. 37 and 38; FIG. 40 is a left side view of the piston shown inFIGS. 37 through 39; FIG. 41 is a bottom view of the piston shown inFIGS. 37 through 40; FIG. 42 is a cutaway view from the right side ofthe piston shown in FIGS. 37 through 41; FIG. 43 is a top plan view ofan assembled cassette using the components shown in FIGS. 1 through 42,with the slide latch in the closed position; FIG. 44 is a bottom view ofthe assembled cassette shown in FIG. 43; FIG. 45 is a front side view ofthe assembled cassette shown in FIGS. 43 and 44; FIG. 46 is a back sideview of the assembled cassette shown in FIGS. 43 through 45; FIG. 47 isa left side view of the assembled cassette shown in FIGS. 43 through 46;FIG. 48 is a right side view of the assembled cassette shown in FIGS. 43through 47; FIG. 49 is a left side view of the latch head used tocapture and actuate the piston; FIG. 50 is a right side view of thelatch head shown in FIG. 49;

FIG. 51 is a bottom view of the latch head shown in FIGS. 49 and 50;

FIG. 52 is a top view of the latch head shown in FIGS. 49 through 51;

FIG. 53 is a cutaway view from the right side of the latch head shown inFIGS. 49 through 52;

FIG. 54 is a right side view of the spring retainer to be mounted in thelatch head shown in FIGS. 49 through 52;

FIG. 55 is a front view of the spring retainer shown in FIG. 54;

FIG. 56 is a left side view of the latch jaw to be mounted on the latchhead shown in FIGS. 49 through 52;

FIG. 57 is a bottom view of the latch jaw shown in FIG. 56;

FIG. 58 is a back view of the latch jaw shown in FIGS. 56 and 57;

FIG. 59 is a left side view of the jaws assembly in the open position,the jaws assembly being made up of the latch head shown in FIGS. 49through 52, the spring retainer shown in FIGS. 54 and 55, the latch jawshown in FIGS. 56 through 58, a latch spring, and pins used to assemblethe various components together;

FIG. 60 is a bottom view of the jaws assembly shown in FIG. 59, with thejaws assembly being shown in the open position;

FIG. 61 is a left side view of the jaws assembly shown in FIGS. 59 and60, with the jaws assembly being shown in the closed position (and inthe open position in phantom lines);

FIG. 62 is a bottom plan view of the main pump unit chassis;

FIG. 63 is a front view of the main pump unit chassis shown in FIG. 62;

FIG. 64 is a top view of the main pump unit chassis shown in FIGS. 62and 63

FIG. 65 is a back view of the main pump unit chassis shown in FIGS. 62through 64;

FIG. 66 is a bottom plan view of the cassette guide used to position thecassette of FIGS. 43 through 48 on the main pump unit;

FIG. 67 is a top view of the cassette guide shown in FIG. 66;

FIG. 68 is a front view of the cassette guide shown in FIGS. 66 and 67;

FIG. 69 is a right side view of the cassette guide shown in FIGS. 66through 68;

FIG. 70 is a left side plan view of the pump shaft on which is mountedthe jaws assembly shown in FIGS. 59 through 61;

FIG. 71 is a right side view plan view of the slide lock used to retainthe cassette shown in FIGS. 43 through 48 in position on the main pumpunit;

FIG. 72 is a bottom view of the slide lock shown in FIG. 71;

FIG. 73 is left side view of the slide lock shown in FIGS. 71 and 72,showing the bevel used to reflect the light beam from the optical lightsource away from the optical light sensor when the slide lock is in theopen position;

FIG. 74 is a top view of the slide lock shown in FIGS. 71 through 73,showing the reflective surface used to reflect the light beam from theoptical light source to the optical light sensor when the slide lock isin the closed position;

FIG. 75 is a front side view of the slide lock shown in FIGS. 71 through74;

FIG. 76 is a back side view of the slide lock shown in FIGS. 71 through75, showing the slanted surface used to reflect the light beam away fromthe corresponding sensor when the slide lock is in the open position;

FIG. 77 is a side view of the power module cam used both to drive thepump through the pump shaft shown in FIG. 70 and to drive the valveactuators;

FIG. 78 is a side view of the power module cam rotated ninety degreesfrom the view of FIG. 77;

FIG. 79 is a bottom view of the power module cam shown in FIGS. 77 and78;

FIG. 80 is a chart of the inlet and outlet valve positions and the pumpdisplacement versus angular position of the power module cam shown inFIGS. 77 through 79;

FIG. 81 is a plan view from the front side of the drive assemblyincluding the motor/cam mount, the motor, the power module cam shown inFIGS. 77 through 79 and the position encoder assembly;

FIG. 82 is a top view of the motor/cam mount included in the driveassembly shown in FIG. 81;

FIG. 83 is a top view of one of the actuator guides used to guide andretain in position the valve actuators for one cassette;

FIG. 84 is a side view of the actuator guide shown in FIG. 83;

FIG. 85 is a side plan view of a valve actuator;

FIG. 86 is an side edge view of the valve actuator shown in FIG. 85;

FIG. 87 is a bottom view of the valve actuator shown in FIGS. 85 and 86;

FIG. 88 is a top plan view of a pressure transducer;

FIG. 89 is a side view of the pressure transducer shown in FIG. 88;

FIG. 90 is a bottom view of the pressure transducer shown in FIGS. 88and 89;

FIG. 91 is a front plan view of an optical sensor module;

FIG. 92 is a side view of the optical sensor module shown in FIG. 91;

FIG. 93 is top view of the optical sensor module shown in FIGS. 91 and92;

FIG. 94 is a bottom view of the optical sensor module shown in FIGS. 91through 93 showing the optical source and sensor pair for detecting theclosed position of the slide lock;

FIG. 95 is a first cutaway view of the optical sensor module shown inFIGS. 91 through 94 showing the optical sources for detecting thecassette identification bits;

FIG. 96 is a second cutaway view of the optical sensor module shown inFIGS. 91 through 94 showing the optical sensors for detecting thecassette identification bits, and the optical source and sensor pair fordetecting air bubbles in the fluid line;

FIG. 97 is a bottom plan view of the elastomeric valve actuator sellused to bias the valve actuators in an upward position;

FIG. 98 is a cutaway view of the valve actuator seal shown in FIG. 97;

FIG. 99 is a bottom view of the main pump unit chassis having thevarious components for one pump mounted thereon, with the slide lock inthe open position ready to receive a cassette;

FIG. 100 is a bottom view of the main pump unit chassis shown in FIG.99, with the slide lock in the closed position as it would be if acassette were installed and latched onto the main pump unit;

FIG. 101 is a top view of the cassette shown in FIGS. 4 through 49 inthe installed position relative to the optical sensor module, with allother parts removed for clarity;

FIG. 102 is a side view of the cassette and optical sensor module ofFIG. 101;

FIG. 103 is a first cutaway view of the cassette and the optical sensormodule of FIGS. 101 and 102, showing a cassette identifying indiciahaving a logical zero value;

FIG. 104 is a second cutaway view of the cassette and the optical sensormodule of FIGS. 101 and 102, showing a cassette identifying indiciahaving a logical one value;

FIG. 105 is a cutaway view from FIG. 99 showing the slide lock in theopen position over the cassette-in-place sensor of the optical sensormodule;

FIG. 106 is a cutaway view from FIG. 105 showing how the slanted surfacereflects the light beam away from the cassette-in-place sensor;

FIG. 107 is a cutaway view from FIG. 100 showing the slide lock in theclosed position over the cassette-in-place sensor of the optical sensormodule, with the light beam being reflected back onto thecassette-in-place sensor;

FIG. 108 is a third cutaway view of the cassette and the optical sensormodule of FIGS. 101 and 102, showing the air-in-line detection apparatusof the preferred embodiment;

FIG. 109 is a cutaway view like FIG. 108, but showing a first alternateair-in-line detection apparatus;

FIG. 110 is a cutaway view like FIG. 108, but showing a second alternateair-in-line detection apparatus;

FIG. 111 is a cutaway view like FIG. 108, but showing a third alternateair-in-line detection apparatus;

FIG. 112 is a cutaway view from the side of the main pump unit chassishaving the various components for one pump mounted thereon and acassette installed, showing the pump drive train;

FIG. 113 is a sectional view of the pump and valves showing thebeginning of the fill cycle;

FIG. 114 is a sectional view of the pump and valves showing thebeginning of the pump cycle;

FIG. 115 is a sectional view of the pressure plateau, the pressurediaphragm, and the pressure transducer;

FIG. 116 is a second sectional view of the pressure plateau, thepressure diaphragm, and the pressure transducer shown in FIG. 115;

FIG. 117 is a somewhat schematic functional diagram of the system of thepresent invention used to provide a pressure signal representingpatient-side pressure and a pressure change rate signal representing therate of change of patient-side pressure from the electrical signalgenerated by the pressure transducer; and

FIG. 118 is a functional diagram of the techniques used to generate anocclusion alarm from the pressure signal and the pressure change ratesignal derived by the circuit of FIG. 117.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The Cassette

The preferred embodiment of the cassette incorporating the pressurediaphragm used with the patient-side occlusion detector of the presentinvention includes all of the features described above in a singlecompact disposable cassette constructed of seven parts. Prior to adiscussion of the construction and operation of the cassette, the basicconstruction of which is the subject of the above-identified patentapplication entitled "Disposable Cassette for a Medication InfusionSystem," it is advantageous to discuss the construction andconfiguration of the seven components included in the cassette. Thefirst of these components and the one around which the other sixcomponents are assembled is a cassette body 100, which is shown in FIGS.1 through 8. The cassette body 100 has an upper surface portion 102which is essentially flat with a number of protrusions and indentationslocated in the top surface thereof (FIG. 1). The upper surface potion102 has a thickness sufficient to accommodate the indentations mentionedabove, some of which are fluid passageways which will be discussedbelow.

Referring generally to FIGS. 1 through 8, a bubble trap 104 is locatedat the front right corner of the cassette body 100 below the uppersurface portion 102, which bubble trap 104 is essentially square incross-section (FIG. 4). The bubble trap 104 includes therein a bubblechamber 106 which is open at the bottom thereof (FIGS. 4, 7, and 8) andclosed at the top by the bottom of the upper surface portion 102 of thecassette body 100. A siphon tube 108 is located in the bubble chamber106, and the siphon tube 108 has an aperture 110 therein leading fromthe bottom of the bubble chamber 106 to the top of the upper surfaceportion 102 of the cassette body 100.

Located behind the bubble trap 104 below the upper surface portion 102of the cassette body 100 on the right side thereof is a pump cylinder112 (FIGS. 3-5, 8). The pump cylinder 112 does to extend downward as faras does the bubble trap 104. The pump cylinder 112, is open on thebottom thereof, and is arranged and configured to receive a piston whichwill be discussed below. The inner configuration of the pump cylinder112 has a main diameter bore 114, with a greater diameter bore 116 nearthe bottom of the pump cylinder 112. The interior of the bottom of thepump cylinder 112 below the greater diameter bore 116 as well as thearea immediately between the greater diameter bore 116 and the maindiameter bore 114 are tapered to facilitate entry of the piston. Themain diameter bore 114 terminates at the top thereof in a frustroconicalsmaller diameter aperture 118 leading to the top of the upper surfaceportion 102 of the cassette body 100 (FIG. 1). The smaller diameteraperture 118 is tapered, having a smaller diameter at the top thereofthan at the bottom.

Extending from on the back side of the exterior of the bubble trap 104facing the pump cylinder 112 are two piston retaining fingers 120 and122 (FIGS. 3 and 4) defining slot therein. The slots defined by the twopiston retaining fingers 120 and 122 face each other, and are open atthe bottoms thereof to accept in a sliding fashion a flat segmentfitting between the two piston retaining fingers 120 and 122. The twopiston retaining fingers 120 and 122 extend from the lower surface ofthe upper surface portion 102 of the cassette body 100 to a locationbetween the bottom of the pump cylinder 112 and the bottom of the bubbletrap 104.

Also extending from the bottom side of the upper surface portion 102 ofthe cassette body 100 are two latch supporting fingers 124 and 126(FIGS. 1-4 and 7). The latch supporting finger 124 extends downwardlyfrom the left side of the bottom of the upper surface portion 102 of thecassette body 100, and at the bottom extends toward the right slightlyto form an L-shape in cross section. The latch supporting finger 124extends toward the front of the cassette body 100 further than does theupper surface portion 102 of the cassette body 100 (FIG. 1), andterminates approximately two-thirds of the toward the back of the uppersurface portion 102 of the cassette body 100.

The latch supporting finger 126 extends downwardly from the bottom ofthe upper surface portion 102 of the cassette body 100 at with the leftside of the bubble trap 104 forming a portion of the latch supportingfinger 126. The latch supporting finger 12 extends toward the leftslightly at the bottom thereof to form a backwards L-shape in crosssection. The latch supporting finger 126 parallels the latch supportingfinger 124, and is equally deep (FIG. 4). The latch supporting fingers124 and 126 together will hold the slide latch, to be described below.

The passageways located in the top of the upper surface portion 102 ofthe cassette body 100 may now be described with primary reference toFIG. 1. The passageways in the top of the upper surface portion 102 areall open on the top side of the upper surface portion 102, and aregenerally U-shaped as they are recessed into the top of the uppersurface portion 102. A first passageway 128 communicates with theaperture 110 in the siphon tube 108 of the bubble trap 104 at one endthereof, and extends toward the back of the upper surface portion 102 ofthe cassette body 100 to a location to the right of the smaller diameteraperture 118 of the pump cylinder 112.

A cylindrical pressure plateau 130 which is essentially circular asviewed from the top extends above the upper surface portion 102 of thecassette body 100 slightly left of the center thereof (best shown inFIGS. 1 through 3, also shown in FIG. 5 through 8). The top of thepressure plateau 130 is flat, with a channel 132 extending across theflat top of the pressure plateau 130. The channel 132 extends from fiveo'clock to eleven o'clock as viewed from the top in FIG. 1, with theback of the cassette body 100 being twelve o'clock. The channel 132 isalso shown in cross-section in FIG. 115, and in a cutaway view in FIG.116. The depth of the channel 132 in the surface of the pressure plateau130 is not quite the height of the pressure plateau 130 above the uppersurface portion 102 of the cassette body 100, with the channel 132gradually becoming deeper with a smooth transition at the edges of thepressure plateau 130 to extend into the upper surface portion 102 of thecassette body 100 (FIG. 116).

A second passageway 134 in the top of the upper surface portion 102 ofthe cassette body 100 begins at location to the left of the smallerdiameter aperture 118 of the pump cylinder 112, and extends toward thefront of the upper surface portion 102 approximately above the latchsupporting finger 126. The second passageway 134 then travels to theleft to connect in fluid communication with the end of the channel 132in the pressure plateau 130 located at five o'clock. A third passageway136 in the top of the upper surface portion 102 of the cassette body 100begins at the end of the channel 132 in the pressure plateau 130 locatedat eleven o'clock, and moves toward the back and left of the cassettebody 100.

At the end of the third passageway 136 is a recessed lens portion 138,which recessed lens portion is used to focus and reflect light used todetect air bubbles passing in front of the recessed lens portion 138.The recessed lens portion 138 is also recessed into the top of the uppersurface portion 102 of the cassette body 100 to allow fluid to passtherethrough. The recessed lens portion 138 is part of the apparatuswhich is the subject of the above-identified patent application entitled"Air-In-Line Detector for a Medication Infusion System." A fourthpassageway 140 in the top of the upper surface portion 102 of thecassette body 100 begins at the other side of the recessed lens portion138 from the third passageway 136, and extends from the left and back ofthe cassette body 100 toward the front and right of the cassette body100 around the pressure plateau 130 to a location at approximately seveno'clock on the pressure plateau 130. It should be noted that the fourthpassageway 140 is spaced away from the pressure plateau 130 to allow forsealing means therebetween.

The end of the fourth passageway 140 terminates at the location at seveno'clock to the pressure plateau 130 in an aperture 142 extending throughthe upper surface portion 102 of the cassette body 100 (FIG. 1). Locatedunderneath the upper surface portion 102 of the cassette body 100concentrically around the aperture 142 is an the outlet tube mountingcylinder -44 (FIGS. 3 and 4) which is in fluid communication with theaperture 142. The outlet tube mounting cylinder 144 extends downwardlyfrom the bottom of the upper surface portion 102 of the cassette body100 to a location above the portions of the latch supporting finger 124and the latch supporting finger 126 extending parallel to the uppersurface 102 of the cassette body 100. A support fin 145 extends to theright from the front of the outlet tube mounting cylinder 144.

Located on top of the upper surface 102 of the cassette body 100 is aslightly raised border 146 (FIG. 1) which completely surrounds the firstpassageway 128, the smaller diameter aperture 118, the second passageway134, the pressure plateau 130, the third passageway 136, the recessedlens portion 138, the recessed lens portion 138, and the fourthpassageway 140. The slightly raised border 146, which is used forsealing purposes, closely surrounds the edges of all of theafore-mentioned segments of the cassette body 100, except as follows.The slightly raised border 146 is spaced away from the portions of thefirst passageway 128 and the second passageway 134 adjacent the smallerdiameter aperture 118, and the smaller diameter aperture 118.

The portions of the slightly raised border 146 around the smallerdiameter aperture 118 resembles a rectangle with its wider sides locatedto the front and back and spaced away from the valve diaphragm 170, andits narrower sides to the right of the portion of the first passageway128 adjacent the smaller diameter aperture 118 and to the left of theportion of the second passageway 134 adjacent the smaller diameteraperture 118. The rectangle is broken only at the locations the firstpassageway 128 and the second passageway 134 extend towards the front ofthe cassette body 100.

The slightly raised border 146 has a segment 147 located between theportion of the first passageway 128 adjacent the smaller diameteraperture 118 and the smaller diameter aperture 118 itself, with thesegment 147 extending between the two wider sides of the rectangle. Theslightly raised border 146 also has another segment 149 located betweenthe portion of the second passageway 134 adjacent the smaller diameteraperture 118 and the smaller diameter aperture 118 itself, with thesegment 149 extending between the two wider sides of the rectangle. Theslightly raised border 146 is also spaced away from the sides of thepressure plateau 130, and the portions of the second passageway 134 andthe third passageway 136 immediately adjacent the pressure plateau 130.

Located at the back of the upper surface 102 of the cassette body 100are three cassette identifying indicia 148, 150, and 152. The first andthird cassette identifying indicia 148 and 152 are small, solidcylinders extending upward from the top of the upper surface 102 of thecassette body -00 (FIGS. 1 and 3). The second cassette identifyingindicia 150 is a prism cut into the bottom of the upper surface 102 ofthe cassette body 100 (FIG. 4). The first, second, and third cassetteidentifying indicia 148, 150, and 152 are the subject of theabove-identified patent application entitled "Cassette OpticalIdentification Apparatus for a Medication Infusion System." It will benoted that the cassette identifying indicia 148, 150, and 152 may be inany order or configuration, and are used for different ID codes toidentify up to eight different cassettes. Additional ID bits could alsobe used if more than eight different cassettes are used. If redundantcodes are desired, the three bits would of course accommodate the use ofless than eight different cassettes.

Completing the construction of the cassette body 100 are five hollowcylinders 154, 156, 158, 160 and 162 protruding from the top surface ofthe upper surface 102 of the cassette body 100, an aperture 161 and aslot 164 located in the top surface o the upper surface 102 of thecassette body 100, and a slot 166 located in the top surface of thelatch supporting finger 124. Four of the hollow cylinders 154, 156, 158,and 160 are located around the pressure plateau 130, with the fifthhollow cylinder 162 being located to the left of the aperture 110 overthe bubble trap 104. The aperture 161 is located in the top surface ofthe upper surface 102 of the cassette body 100 in front and to the rightof center of the pressure plateau 130. The slot 164 is located in thetop surface of the upper surface 102 of the cassette body 100 near theback and the right side thereof. The slot 166 is located in the topsurface of the latch supporting finger 124 near the front of thecassette body 100.

Referring now to FIGS. 9 through 12, a valve diaphragm 170 is shownwhich is arranged and configured to fit over the top of the uppersurface 102 of the cassette body 100 (FIG. 1). The valve diaphragm 170is made of flexible, resilient material, such as a medical gradesilicone rubber. The hardness of the material used for the valvediaphragm 170 would be between thirty and fifty on the Shore A scale,with the preferred embodiment utilizing a hardness of approximatelythirty-five to forty. The valve diaphragm 170 has three primaryfunctions, the first of which is to seal the tops of the first, second,third, and fourth passageways 128, 134, 136, and 140, respectively.Accordingly, the main surface of the valve diaphragm 170 is flat, and issized to fit over the first, second, third, and fourth passageways 128,134, 136, and 140, respectively, and also over the entire slightlyraised border 146. The flat portion of the valve diaphragm 170 has threeapertures 172, 174, and 176, and a notch 175 therein to accommodate thehollow cylinders 156, 160, and 162 and a pin fitting into the aperture161 (FIG. 1), respectively, and to align the valve diaphragm 170 inposition over the top of the upper surface 102 of the cassette body 100.It should be noted that the valve diaphragm 170 does not necessarilysurround the other two hollow cylinders 154 and 158.

The second primary function of the valve diaphragm 170 is to provideboth an inlet valve between the first passageway 128 and the smallerdiameter aperture 118 leading to the pump cylinder 112, and to providean outlet valve between the smaller diameter aperture 118 leading to thepump cylinder 112 and the second passageway 134. To fulfill thisfunction the valve diaphragm 170 has an essentially rectangular domedportion 178 (shown in plan view in FIGS. 9 and 10, and incross-sectional views in FIGS.

and 12) forming a cavity 180 in the bottom of the valve diaphragm 170.When the valve diaphragm 170 is installed in position on the top of theupper surface 102 of the cassette body 100, the cavity 180 will belocated just inside the rectangular portion of the slightly raisedborder 146 around the smaller diameter aperture 118 leading to the pumpcylinder 112 (FIG.

The cavity 180 will therefore be in fluid communication with the firstpassageway 128, the smaller diameter aperture 118 leading to the pumpcylinder 112, and the second passageway 134. Prior to installation ofthe cassette onto the main pump unit, the cavity 180 allows the openfluid path to facilitate priming of the cassette, where all air isremoved from the system. Once primed, the cassette may be inserted ontothe main pump unit and the cavity 180 will contact valve actuators toprevent free flow through the cassette. By using an inlet valve actuatorto force the domed portion 178 over the segment 147 of the slightlyraised border 146 (FIG. 1), the flow of fluids between the firstpassageway 128 and the smaller diameter aperture 118 will be blocked,but the flow of fluids between the smaller diameter aperture 118 and thesecond passageway 134 will be unaffected. Likewise, by using an outletvalve actuator to force the domed portion 178 over the segment 149 ofthe slightly raised border 146 (FIG. 1), the flow of fluids between thesmaller diameter aperture 118 and the second passageway 134 will beblocked, but the flow of fluids between the first passageway 128 and thesmaller diameter aperture 118 will be unaffected. Extending around andspaced away from the front and sides of the domed portion 178 on the topsurface of the valve diaphragm 170 is a Ushaped raised rib 181, the legsof which extend to the back of the valve diaphragm 170 (FIG. 9).

The third primary function of the valve diaphragm 170 is to provide apressure diaphragm which may be used to monitor outlet fluid pressure.Accordingly, the valve diaphragm 170 has a pressure diaphragm 182 whichis supported atop an upper cylindrical segment 184, which in turn islocated atop a lower cylindrical segment 186 extending above the surfaceof the valve diaphragm 170. The upper cylindrical segment 184 and thelower cylindrical segment 186 have identical inner diameters, with alower cylindrical segment 186 having a greater outer diameter than theupper cylindrical segment 184. A portion of the top of the lowercylindrical segment 186 extends outwardly around the bottom of the uppercylindrical segment 184, creating a lip 188. In the preferredembodiment, the pressure diaphragm 182 may be domed slightly, as seen inFIG. 11.

Turning now to FIGS. 13 through 23, a retainer cap 190 is shown whichfits over the valve diaphragm 170 after it is mounted on the top of theupper surface 102 of the cassette body 100. The retainer cap 190 thusfunctions to cover the top of the cassette body 100, retaining the valvediaphragm 170 between the retainer cap 190 and the cassette body 100 ina sealing fashion. The retainer cap 190 thus has the same generaloutline when viewed from the top (FIG. 13) as the cassette body 100(FIG. 1). Located in the bottom of the retainer cap 190 (FIG. 14) aresix pins 192, 194, 196, 198, 200, and 199, which are to be received bythe hollow cylinders 154, 156, 158, 160, and 162 and the aperture 161,respectively, in the cassette body 100 to align the retainer cap 190 onthe cassette body 100. Also located in the bottom of the retainer cap190 is a tab 202 to be received by the slot 164, and a tab 204 to bereceived by the slot 166.

The retainer cap 190 has three apertures 206, 208, and 210 therethroughlocated to coincide with the locations of the first cassette identifyingindicia 148, the second cassette identifying indicia 150, and the thirdcassette identifying indicia 152, respectively. The size of the threeapertures 206, 208, and 210 is sufficient to receive the small, solidcylinders which the first cassette identifying indicia 148 and the thirdcassette identifying indicia 152 comprise.

Located in the retainer cap 190 is a rectangular aperture 212 (FIGS. 13,14, 19 and 20) for placement over the domed portion 178 on the valvediaphragm 170. The rectangular aperture 212 in the retainer cap 190 isslightly larger than the domed portion 178 on the valve diaphragm 170 toprevent any closure of the cavity 180 formed by the domed portion 178when th retainer cap 190 is placed over the valve diaphragm 170 and thecassette body 100. The domed portion 178 of the valve diaphragm 170therefore will protrude through the rectangular aperture 212 in theretainer cap 190. In the bottom of the retainer cap 190 around therectangular aperture 212 is a U-shaped groove 214 (FIG. 14) designed toaccommodate the U-shaped raised rib 181 on the valve diaphragm 170.

Also located in the retainer cap 190 is a circular aperture 216 (FIGS.13 and 14), which has a diameter slightly larger than the outer diameterof the upper cylindrical segment 184 on the valve diaphragm 170, toallow the upper cylindrical segment 184 and the pressure diaphragm 182to protrude from the circular aperture 216 in the retainer cap 190. Thediameter of the circular aperture 216 is smaller than the outer diameterof the lower cylindrical segment 186 on 170, and on the bottom of theretainer cap 190 is disposed concentrically around the circular aperture216 a cylindrical recess 218 to receive the lower cylindrical segment186 on the valve diaphragm 170. Disposed in the cylindrical recess 218on the bottom side of the retainer cap 190 is a circular raised bead 220(FIGS. 14, 19, and 21) to help in the sealing of the cassette as it isassembled.

The retainer cap 190 has a front edge 222 (FIG. 16), a back edge 224(FIG. 15), and left (FIG. 18) and right (FIG. 17) side edges 226 and228, respectively. The edges 222, 224, 226, and 228 will contact the topof the upper surface 102 of the cassette body 100 when the retainer cap190 is assembled onto the cassette body 100 with the valve diaphragm 170disposed therebetween. The retainer cap 190 is attached to the cassettebody -00 in the preferred embodiment by ultrasonic welding, butadhesives or other bonding techniques known in the art may also be used.

Referring next to FIGS. 22 through 26, a bubble chamber cap 230 isillustrated which is for placement onto the open bottom of the bubbletrap 104 (FIG. 4). The bubble chamber cap 230 is on the bottom (FIG. 23)the same size as the outer edges of the bottom of the bubble trap 104(FIG. 4), and has a tab 232 (FIGS. 22 through 24) on the bottom whichwill project toward the back of the cassette beyond the back edge of thebubble trap 104. The bubble chamber cap 230 has a rectangular wallportion 234 (FIG. 24) extending upward from the bottom of the bubblechamber cap 230 and defining therein a square space, which rectangularwall portion 234 is sized to fit inside the bubble chamber 106 (FIG. 4).

Located at the front and left sides of the rectangular wall portion 234and extending upwards from the bottom of the bubble chamber cap 230 isan inlet cylinder 236 (FIGS. 22, 24, and 26) having an inlet aperture238 extending therethrough. The inlet aperture 238 extends through thebottom of the bubble chamber cap 230 (FIGS. 23 and 25), and is designedto receive from the bottom of the bubble chamber cap 230 a length oftubing therein. The bubble chamber cap 230 is attached to the bottom ofthe bubble trap 104 in the cassette body 100 in the preferred embodimentby ultrasonic welding, but adhesives or other bonding techniques knownin the art may also be used.

When the bubble chamber cap 230 is mounted to the bubble trap 104, theinlet cylinder 236 extends up to at least half of the height of thebubble chamber 106 (FIG. 7), and the siphon tube 108 (FIG. 7) drawsfluid from the bottom of the siphon tube 108 in the space within therectangular wall portion 234 of the bubble chamber cap 230 (FIG. 26). Itwill be appreciated by those skilled in the art that fluid will enterthe bubble chamber 106 through the inlet aperture 238 in the inletcylinder 236 near the top of the siphon tube 108, maintaining all airbubbles above the level near the bottom of the bubble chamber 106 atwhich fluid is drawn from the bubble chamber 106 by the siphon tube 108.

Moving now to FIGS. 27 through 32, a slide latch 240 is disclosed whichserved two main functions in the cassette. The slide latch 240 firstserves to latch the cassette into place in a main pump unit. It alsoserves to block the flow of fluid through the cassette when it is notinstalled, with the closing of the slide latch 240 to lock the cassetteinto place on the main pump unit also simultaneously allowing the flowof fluid through the cassette. The slide latch 240 slides from the frontof the cassette body 100 (FIG. 2) between the latch supporting finger124 and the latch supporting finger 126.

The slide latch 240 has an essentially rectangular, flat front portion242 (FIG. 31) which is of a height equal to the height of the cassettebody 100 with the retainer cap 190 and the bubble chamber cap 230installed, and a width equal to the distance between the left side ofthe bubble trap 104 and the left side of the cassette body 100. Twosmall notches 244 and 246 are removed from the back side of the frontportion 242 at the top thereof (FIGS. 27, 28, and 30), the small notch244 being removed at a location near the left corner, and the smallnotch 246 being removed at the right corner.

Extending from the back side of the front portion 242 aboutthree-quarters of the way down towards the back is a horizontal bottomportion 248 (FIG. 29), which has its edges directly below the closestedges of the small notch 244 and the small notch 246. Extending from theinner edge of the small notch 244 at the top of the slide latch 240 downto the bottom portion 248 is an inverted angled or L-shaped portion 250.Similarly, extending from the inner edge of the small notch 246 at thetop of the slide latch 240 down to the bottom portion 248 is aninverted, backwards angled or L-shaped portion 252 (FIGS. 27 and 28).

Spaced outwardly from the left side of the bottom portion 248 and theleft side of the leg of the inverted L-shaped portion 250 is a leftslide side 254. Likewise, spaced outwardly from the right side of thebottom portion 248 and the right side o the leg of the inverted,backwards L-shaped portion 252 is a right slide side 256 (FIGS. 28 and30). The left and right slide sides 254 and 256 are located slightlyabove the bottom of the bottom portion 248 (FIG. 30). The left and rightslide sides 254 and 256 are of a height to be engaged in the latchsupporting finger 124 and the latch supporting finger 126 (FIG. 2),respectively.

Located in the bottom portion 248 is an elongated, tear-shaped aperture258 (FIG. 29), with the wider portion thereof toward the front of theslide latch 240 and the extended narrower portion thereof toward theback of the slide latch 240. When the slide latch 240 is inserted intothe latch supporting finger 124 and the latch supporting finger 126 onthe cassette body 100, and the slide latch 240 is pushed fully towardthe back of the cassette body 100, the wider portion of the elongated,tear-shaped aperture 258 will be aligned with the aperture 142 in theoutlet tube mounting cylinder 144 (FIG. 4) to allow a segment of tubing(not shown) leading from the aperture 142 to be open. When the slidelatch 240 is pulled out from the front of the cassette body 100, thesegment of tubing (not shown) will be pinched off by the narrowerportion of the elongated, tear-shaped aperture 258.

It is critical that the design and location of the elongated,tear-shaped aperture 258 in the slide latch 240 ensure that the slidelatch 240 engages the main pump unit before the tubing is opened up, andfluid is allowed to flow through the cassette. Likewise, the tubing mustbe pinched off and the fluid path through the cassette must be blockedbefore the slide latch 240 releases the cassette from the main pumpunit. In addition, the choice of material for the slide latch 240 isimportant, with a lubricated material allowing the pinching operation tooccur without damaging the tubing (not shown). Examples of suchmaterials are silicone or Teflon impregnated acetals such as Delren.

Located at the back of the slide latch 240 on the inside of the rightslide side 256 at the bottom thereof is a tab 257 (FIGS. 27, 30, and 32)which is used to engage the main pump unit with the cassette when theslide is closed. Located on the top side of the bottom portion 248 tothe right of the elongated, tear-shaped aperture 258 is a smallwedge-shaped retaining tab 259 (FIG. 27, 30, and 32). The retaining tab259 cooperates with the bottom of the slightly raised border 146 of thecassette body 100 (FIG. 2), to resist the slide latch 240 from beingfreely removed once installed into the cassette body 100. When the slidelatch 240 is pulled back out from the front of the cassette body 100 sothat the wider portion of the elongated, tear-shaped aperture 258 isaligned with the aperture 142 in the outlet tube mounting cylinder 144,the retaining tab 259 will engage the slightly raised border 146 (FIGS.2 and 4), resisting the slide latch 240 from being drawn further out.

Referring now to FIGS. 33 through 36, a one-piece piston cap and bootseal 260 is illustrated, which is the subject of the above-identifiedpatent application entitled "Piston Cap and Boot Seal for a MedicationInfusion System," and which is for use on and in the pump cylinder 112(FIGS. 3 and 8). The piston cap and boot seal 260 is of one-piececonstruction, and is made of flexible, resilient material, such assilastic (silicone rubber) or medical grade natural rubber. Naturalrubber may be used to minimize friction, since some sticking of asilicone rubber piston cap and boot seal 260 in the pump cylinder 112(FIG. 8) may occur. Teflon impregnated silastic or other proprietaryformulas widely available will overcome this problem. In addition, thepiston cap and boot seal 260 may be lubricated with silicone oil priorto installation in the pump cylinder 112. The advantage of usingsilastic is that it may be radiation sterilized, whereas natural rubbermust be sterilized using gas such as ethylene oxide. In addition,silastic has better wear characteristics than natural rubber, making itthe preferred choice.

The piston cap and boot seal 260 includes a piston cap portion indicatedgenerally at 262, and a boot seal portion comprising a retaining skirt264 and a thin rolling seal 266. The piston cap portion 262 includes ahollow cylindrical segment 268 having an enlarged, rounded piston caphead 270 located at the top thereof. The piston cap head 270 has aroughly elliptical cross-section, with an outer diameter on the sidessufficient to provide a dynamic seal in the main diameter bore 114 ofthe pump cylinder 112 (FIG. 8). The roughly elliptical configuration ofthe piston cap head 270 closely fits the top of the main diameter bore114 of the pump cylinder 112. Extending from the top of the piston caphead 270 at the center thereof is a frustroconical segment 272, with thelarger diameter of the frustroconical segment 272 being at the bottomthereof attached to the piston cap head 270. The frustroconical segment272 is of a size to closely fit in the smaller diameter aperture 118 ofthe pump cylinder 112 (FIG. 8).

The hollow cylindrical segment 268 and the piston cap head 270 togetherdefine a closed end of the piston cap and boot seal 260 to receive apiston, which will be described below. The hollow cylindrical segment268 has located therein a smaller diameter portion 274, which smallerdiameter portion 274 is spaced away from the bottom of the piston caphead 270 to provide retaining means to retain a piston in the hollowcylindrical segment 268 between the piston cap head 270 and the smallerdiameter portion 274.

The retaining skirt 264 is essentially cylindrical, and is designed tofit snugly around the outer diameter of the pump cylinder 112 (FIG. 8).Prior to installation and with the piston cap and boot seal 260 in arelaxed configuration as shown in FIGS. 33 through 36, the retainingskirt 264 is located roughly around the hollow cylindrical segment 268.The retaining skirt 264 has an internal diameter sufficiently small toretain the retaining skirt 264 in position around the pump cylinder 112(FIG. 8) without moving when the piston cap portion 262 moves.

Located around the inner diameter of the retaining skirt 264 is atortuous path 276 leading from one end of the retaining skirt 264 to theother. The tortuous path 27 is required for sterilization of theassembled cassette, to allow the sterilizing gas to sterilize the areabetween the inside of the pump cylinder 112 and the piston cap and bootseal 260, which would be closed and may remain unsterilized if thetortuous path 276 did not exist. In addition, since the sterilizing gasis hot and cooling occurs rapidly after the sterilizing operation, thetortuous path 276 allows pressure equalization to occur rapidly where itotherwise would not. In the preferred embodiment, the tortuous path 276is a series of threads in the inner diameter of the retaining skirt 264.

Completing the construction of the piston cap and boot seal 260 is therolling seal 266, which is a segment defined by rotating around thecenterline of the piston cap and boot seal 260 a U having a first leg atthe radius of the hollow cylindrical segment 268 and a second leg at theradius of the retaining skirt 264, with the top of the first leg of theU being attached to the bottom of the hollow cylindrical segment 268 andthe top of the second leg of the U being attached to the bottom of theretaining skirt 264. When the piston cap and boot seal 260 is installedand the piston cap portion 262 moves in and out in the main diameterbore 114 in the pump cylinder 12 (FIG. 8), the legs of the U will varyin length, with one leg becoming shorter as the other leg becomeslonger. In this manner, the rolling seal 266 provides exactly what itsname implies--a seal between the piston cap portion 262 and theretaining skirt 264 which rolls as the piston cap portion 262 moves.

Referring now to FIGS. 37 through 42, a piston assembly 280 is shownwhich drives the piston cap portion 262 of the piston cap and boot seal260 (FIG. 36) in the pump cylinder 112 (FIG. 8). The piston assembly 280has a rectangular base 282 which is positioned horizontally and locateddirectly behind the bubble chamber cap 230 (FIG. 24) when the piston capportion 262 is fully inserted into the pump cylinder 112. Therectangular base 282 has a notch 284 (FIGS. 41 and 42) in the front edgethereof, which notch is slightly larger than the tab 232 in the bubblechamber cap 230 (FIG. 23).

Extending upward from the front edge of the rectangular base 282 on theleft side of the notch 284 is an arm 286, and extending upward from thefront edge of the rectangular base 282 on the right side of the notch284 is an arm 288. At the top of the arms 286 and 288 is a verticallyextending rectangular portion 290 (FIG. 38). The rectangular portion 290as well as the upper portions of the arms 286 and 288 are for insertioninto and between the piston retaining finger 120 and the pistonretaining finger 122 in the cassette body100 (FIG. 4).

The top of the rectangular portion 290 will contact the bottom of theupper surface 102 of the cassette body 100 (FIG. 8) to limit the upwardmovement of the piston assembly 280, the rectangular base 282 beingapproximately even with the bubble chamber cap 230 (FIG. 24) installedin the bottom of the bubble trap 104 of the cassette body 100 when thepiston assembly 280 is in its fully upward position. The bottom of therectangular portion 290 (FIG. 42) will contact the tab 232 on the bubblechamber cap 230 (FIG. 24) when the piston assembly 280, the piston head296, and the piston cap portion 262 (FIG. 36) are fully retracted fromthe pump cylinder 112 (FIG. 8).

Extending upwards from the top of the rectangular base 282 near the backedge of the rectangular base 282 and located centrally with respect tothe side edges of the rectangular base 282 is a cylindrical piston rod292. At the top of the piston rod 292 is a reduced diameter cylindricalportion 294, and mounted on top of the reduced diameter cylindricalportion 294 is a cylindrical piston head 296. The diameter of the pistonhead 296 is larger than the diameter of the reduced diameter cylindricalportion 294, and the top of the piston head 296 has rounded edges in thepreferred embodiment. The piston head 296 is designed to be received inthe portion of the hollow cylindrical segment 268 between the smallerdiameter portion 274 and the piston cap head 270 in the piston capportion 262 (FIG. 36). The reduced diameter cylindrical portion 294 islikewise designed to be received in the smaller diameter portion 274 ofthe piston cap portion 262.

The top of the piston head 296 is slightly above the top of therectangular portion 290, and when the piston assembly 280 is in itsfully upward position, the piston head 296 will have brought the pistoncap head 270 and the frustroconical segment 272 thereon (FIG. 36) to thetop of the pump cylinder 112 and into the smaller diameter aperture 118(FIG. 8), respectively, to completely eliminate volume both within thepump cylinder 112 and within the smaller diameter aperture 118.

Completing the construction of the piston assembly 280 are two raisedbeads 298 and 300, with the raised bead 298 being on the top surface ofthe rectangular base 282 on the left side of the piston rod 292, and theraised bead 300 being on the top surface of the rectangular base 282 onthe right side of the piston rod 292. Both of the raised beads 298 and300 extend from the sides of the piston rod 292 laterally to the sidesof the rectangular base 282. The raised beads 298 and 300 will be usedto center the piston assembly 280 with the jaws of the main pump unitused to drive the piston assembly 280, as well as to facilitateretaining the piston assembly 280 in the jaws.

The assembly and configuration of the cassette may now be discussed,with reference to an assembled cassette 302 in FIGS. 43 through 48, aswell as to other figures specifically mentioned in the discussion. Thevalve diaphragm 170 is placed over the top of the upper surface 102 ofthe cassette body 100, with the apertures 172, 174, and 176 placed overthe hollow cylinders 156, 160, and 162, respectively. The retainer cap190 is then located over the valve diaphragm 170 and the cassette body100, and is secured in place by ultrasonic welding. Note again thatwhile adhesive sealing may be used, it is more difficult to ensure theconsistent hermetic seal required in the construction of the cassette302.

The step of firmly mounting the retainer cap 190 onto the cassette body100 exerts a bias on the valve diaphragm 170 (FIG. 9) causing it to becompressed in certain areas, particularly over the slightly raisedborder 146 on the top surface of the upper surface 102 of the cassettebody 100 (FIG. 1). This results in excellent sealing characteristics,and encloses the various passageways located in the upper surface 102 ofthe cassette body 100. The first passageway 128 is enclosed by the valvediaphragm 170, communicating at one end thereof with the aperture 110and at the other end thereof with the area between the cavity 180 andthe upper surface 102 of the cassette body 100. The second passageway134 also communicates with the area between the cavity 180 and the uppersurface 102 of the cassette body 100 at one end thereof, with the otherend of the second passageway 134 communicating with one end of thepassageway 132 in the pressure plateau 130.

The pressure diaphragm 182 is located above the surface of the pressureplateau 130 (FIGS. 115 and 116), and a space exists between the edges atthe side of the pressure plateau 130 and the inner diameters of theupper cylindrical segment 184 and the lower cylindrical segment 186.This allows the pressure diaphragm 182 to be quite flexible, a designfeature essential to proper operation of the pressure monitoringapparatus. It may therefore be appreciated that the flow area betweenthe second passageway 134 and the third passageway 136 is not just thearea of the passageway 132, but also the area between the pressurediaphragm 182 and the pressure plateau 130, as well as the area aroundthe sides of the pressure plateau 130 adjacent the upper cylindricalsegment -84 and the lower cylindrical segment 186.

The third passageway 136 (FIG. 1) is also enclosed by the valvediaphragm 170 (FIG. 9), and communicates at one end with the other endof the passageway 132, and at the other end with the recessed lensportion 138. The fourth passageway 140 is enclosed by the valvediaphragm 170, and communicates at one end with the recessed lensportion 138 and at the other end with the aperture 142.

Next, the bubble chamber cap 230 is placed on the bottom of the bubblechamber 106, as shown in FIG. 44, and is secured by ultrasonicallysealing the bubble chamber cap 230 to the cassette body 100. The pistoncap portion 262 of the piston cap and boot seal 260 (FIG. 36) isinserted into the main diameter bore 114 of the pump cylinder 112 (FIG.8), and pushed toward the top of the main diameter bore 114.Simultaneously, the retaining skirt 264 is placed over the outside ofthe pump cylinder 112 and is moved up the outer surface of the pumpcylinder 112 to the position shown in FIGS. 46 and 48, which is nearlyto the top of the outer surface of the pump cylinder 112. Next, thepiston head 296 of the piston assembly 280 (FIGS. 37 and 40) is insertedinto the hollow cylindrical segment 268 of the piston cap and boot seal260, and is forced past the smaller diameter portion 274 until it snapshome, resting against the bottom of the piston cap head 270.

The slide latch 240 is then inserted into engagement with the cassettebody 100, which is accomplished by sliding the left slide side 254 intothe latch supporting finger 124 on the right side thereof and by slidingthe right slide side 256 into the latch supporting finger 126 on theleft side thereof. The slide latch 240 is then pushed fully forward toalign the wider portion of the elongated, tear-shaped aperture 258 withthe outlet tube mounting cylinder 144. An inlet tube 304 is adhesivelysecured in the inner diameter of the inlet aperture 238 in the bubblechamber cap 230, in fluid communication with the bubble chamber 106. Anoutlet tube 306 extends through the wider portion of the elongated,tear-shaped aperture 258 and is adhesively secured in the inner diameterof the outlet tube mounting cylinder 144 in the cassette body 100, influid communication with the fourth passageway 140 through the aperture142.

The inlet tube 304 and the outlet tube 306 are shown in the figures onlyin part; on their respective ends not connected to the assembledcassette 302 they may have connector fittings such as standard luerconnectors (not shown), which are well known in the art. The use ofadhesives to attach the inlet tube 304 and the outlet tube 306 to theassembled cassette 302 also utilizes technology well known in the art.For example, adhesives such as cyclohexanone, methylene dichloride, ortetrahydrofuron (THF) may be utilized.

The Main Pumo Unit

The preferred embodiment of the main pump unit used with the pressurediaphragm of the aboveidentified copending application entitled"Pressure Diaphragm for a Medication Infusion System" includes a numberof components used to hold, latch, and drive the cassette describedabove. Referring first to FIGS. 49 through 53, a latch head 310 isillustrated which is used to grasp the raised bead 298 and the raisedbead 300 of the piston assembly 280 (FIG. 37). Extending from the frontof the latch head 310 at the top thereof on the left side is a left jaw312, and extending from the front of the latch head 310 at the topthereof on the right side is a right jaw 314. The left and right jaws312 and 314 have curved indentations on the bottom sides thereof toreceive the raised bead 298 and the raised bead 300 (FIG. 37),respectively. A space between the left jaw 312 and the right jaw 314allows them to fit around the piston rod 292 of the piston assembly 280.

A cylindrical aperture 316 is located in the top of the latch head 310,which cylindrical aperture 316 is designed to receive a shaft on whichthe latch head 310 is mounted. A threaded aperture 318 in the back sideof the latch head 310 communicates with the cylindrical aperture 316,and will have locking means installed therein to lock a shaft in thecylindrical aperture 316. An aperture 320 extends through the latch head310 rom the left side to the right side thereof near the back and bottomof the latch head 310.

A notch 322 is located in the latch head 310 at the bottom and frontthereof and in the center thereof, leaving a side portion 324 on theleft side and a side portion 326 on the right side. An aperture 328 islocated through the side portion 324, and an aperture 330 is locatedthrough the side portion 326, which apertures 328 and 330 are aligned.In addition, the portion of the latch head 310 including the left jaw312 has a raised edge 327 facing upward and backward, and a raised edge329 facing down and forward. The portion of the latch head 310 includingthe right jaw 314 has a raised edge 331 facing downward and forward. Theraised edges 327, 329, and 331 will be used to limit the movement of thelatch jaw, which will be discussed below.

A spring seat 332 is shown in FIGS. 54 and 55, which is designed to fitin the notch 322 in the latch head 310 (FIGS. 51 and 53). The springseat 332 has an aperture 334 extending therethrough from the left sideto the right side, which aperture 334 is slightly larger than theapertures 328 and 330 in the latch head 310. The spring seat 332 alsohas a cylindrical segment 336 extending from the front side thereof.

A latch jaw 340 is illustrated in FIGS. 56 through 58, which latch jaw340 is used to grasp the bottom of the rectangular base 282 of thepiston assembly 280 (FIG. 37) and maintain the left and right jaws 312and 314 of the latch head 310 (FIG. 51) in contact with the raised bead298 and the raised bead 300, respectively. The latch jaw 340 has a frontjaw portion 342 approximately as wide a the left and right jaws 312 and314 of the latch head 310, which jaw portion 342 is the portion of thelatch jaw 340 which contacts the bottom of the rectangular base 282 ofthe piston assembly 280. Extending back from the left side of the jawportion 342 is a left arm 344, and extending back from the right side ofthe jaw portion 342 is a right arm 346.

The left arm 344 has an aperture 348 (not shown) therethrough from theleft side to the right side at the end of the left arm 344 away from thejaw portion 342. Likewise, the right arm 346 has an aperture 350therethrough from the left side to the right side at the end of theright arm 346 away from the jaw portion 342. The apertures 348 and 350are slightly smaller in diameter than the aperture 320 in the latch head310 (FIGS. 49 and 50).

Extending upward from and at an approximately sixty degree angle withrespect to the right arm 346 from the end of the right arm 346 away fromthe jaw portion 342 is a driving arm 352. At the end of the driving arm352 which is not attached to the right arm 346 is a link pin 354extending to the right. Completing the construction of the latch jaw 340is a cylindrical recess 356 located in the back side of the jaw portion342, which cylindrical recess 356 has an inner diameter larger than theouter diameter of the cylindrical segment 336 of the spring seat 332(FIG. 55).

Referring now to FIGS. 59 through 61, the construction of a jawsassembly 360 from the latch head 310, the spring seat 332, and the latchjaw 340 is illustrated. The spring seat 332 fits within the notch 322and between the left jaw 312 and the right jaw 314 of the latch head310. A pin 362 is inserted through the aperture 328 in the side portion324, the aperture 334 in the spring seat 332, and the aperture 330 inthe side portion 326. The pin 362 is sized to fit snugly in theapertures 328 and 330, thereby retaining the pin 362 in place andallowing the spring seat 332 to rotate about the pin 362.

The latch jaw 340 is mounted onto the latch head 310 with the left jaw312 and the right jaw 314 of the latch head 310 facing the jaw portion342 of the latch jaw 340 using a pin 364. The pin 364 is insertedthrough the aperture 348 (not shown) in the left arm 344, the aperture320 in the latch head 310, and the aperture 350 in the right arm 346.The pin 364 is sized to fit snugly in the apertures 348 and 350, therebyretaining the pin 364 in place and allowing the latch jaw 340 to rotateabout the pin 364.

A spring 366 has one end thereof mounted over the cylindrical segment336 on the spring seat 332, and the other end thereof mounted in thecylindrical recess 356 in the latch jaw 340. The spring 366 acts to biasthe latch jaw 340 in either the open position shown in FIG. 59 with thejaw portion 342 of 340 away from the left jaw 312 and the left jaw 312of the latch head 310, or in the closed position shown in FIG. 61, withthe jaw portion 342 of the latch jaw 340 urged closely adjacent the leftjaw 312 and the right jaw 314 of the latch head 310. The movement of thelatch jaw 340 in both directions with respect to the latch head 310 islimited, to the position shown in FIG. 59 by the driving arm 352contacting the raised edge 327, and to the position shown in FIG. 61 bythe right arm 346 contacting the raised edge 329 and by the left arm 344contacting the raised edge 331. When the assembled cassette 302 isinstalled, movement of the latch jaw 340 to the position of FIG. 61 willalso be limited by the presence of the piston assembly 280, with therectangular base 282 being grasped by the jaws assembly 360. It will benoted that by moving the pin 354 either toward the front or toward theback, the latch jaw 340 may either be opened or closed, respectively.

Referring next to FIGS. 62 through 65, a main pump unit chassis 370 isillustrated which is designed to mount three independent pump unitsincluding three drive mechanisms into which three disposable assembledcassettes 302 may be installed. The assembled cassettes 302 are mountedon the bottom side of the pump chassis 370 shown in FIG. 62, with themotors and drive train being mounted on top of the pump chassis 370(FIG. 64) and being installed in a housing (not shown) mounted on top ofthe pump chassis 370.

Located on the pump chassis 370 are three pairs of angled segments 372and 374, 376 and 378, and 380 and 382. Each pair of angled segments 372and 374, 376 and 378, and 380 and 382 defines two facing channelstherebetween. In the preferred embodiment, the angled segments 372 and374, 376 and 378, and 380 and 382 are angled slightly further from thebottom of the pump chassis 370 near the front, to thereby have a cammingeffect as the assembled cassette 302 is installed and the slide latch240 is closed. Specifically, the angled segment 372 defines a channelfacing the angled segment 374, and the angled segment 374 defines achannel facing the angled segment 372. The angled segment 376 defines achannel facing the angled segment 378, and the angled segment 278defines a channel facing the angled segment 376. Finally, the angledsegment 380 defines a channel facing the angled segment 382, and theangled segment 382 defines a channel facing the angled segment 380.

Each of the pairs of angled segments 372 and 374, 376 and 378, and 380and 382 provides means on the bottom of pump chassis 370 for oneassembled cassette 302 to be securely latched to. The inverted L-shapedportion 250 and the inverted, backwards L-shaped portion 252 in theslide latch 240 (FIGS. 29 and 30) of the assembled cassette 302 aredesigned to facilitate attachment to one of the pairs of angled segments372 and 374, 376 and 378, and 380 and 382. With the slide latch 240pulled back away from the front of the assembled cassette 302 an areabetween the front portion 242 of the slide latch 240 and the top frontof the cassette body 100 and the retainer cap 190 is open, allowing thetop of the assembled cassette 302 to be placed over one of the pairs ofangled segments 372 and 374, 376 and 378, and 380 and 382.

By way of example, assume that the assembled cassette 302 is to bemounted in the first position (the position on the left end of the pumpchassis 370) on the first pair of angled segments 372 and 374. The topsurface of the assembled cassette 302, which is the retainer cap 190(FIG. 43), will mount against the bottom of the pump chassis 370 (FIG.62). In order to place the assembled cassette 302 in condition to beinstalled, the slide latch 240 is pulled back fully from the front ofthe assembled cassette 302, leaving an area between the front portion242 of the slide latch 240 and the front top portion of the assembledcassette 302 (made up of the cassette body 100 and the retainer cap 190)facing the front portion 242 of the slide latch 240.

The top of the assembled cassette 302 is then placed against the bottomof the pump chassis 370 with the first pair of angled segments 372 and374 fitting in the area between the front portion 242 of the slide latch240 and the front top portion of the assembled cassette 302. The slidelatch 240 is then pushed forward into the cassette body 100, sliding theinverted L-shaped portion 250 of the slide latch 240 into engagementwith the angled segment 372, and sliding the inverted, backwardsL-shaped portion 252 of the slide latch 240 into engagement with theangled segment 374. The assembled cassette 302 will thus be held inposition on the bottom of the pump chassis 370 until the slide latch 240is again pulled back, releasing the assembled cassette 302.

Projecting from the bottom of the pump chassis 370 are a number ofsegments used to position and align the assembled cassettes 302 in thefirst (the position on the left end of the pump chassis 370), second(intermediate), and third (the position on the right end of the pumpchassis 370) positions on the pump chassis 370. Three left lateralsupport walls 384, 386, and 388 protrude from the bottom of the pumpchassis 370 at locations to support the upper left side portion of theassembled cassettes 302 near the back thereof in proper positions in thefirst, second, and third positions, respectively. Likewise, three rightlateral support walls 390, 392, and 394 protrude from the bottom of thepump chassis 370 at locations to support the rear-most extending upperportion of the assembled cassettes 302 on the right side thereof inproper positions in the first, second, and third positions,respectively.

Additional support and positioning for the installation of the assembledcassettes 302 into the first, second, and third positions are providedfor the upper right back corner of the assembled cassettes 302 by threeright corner support walls 396, 98, and 400, respectively. The threeright corner support walls 96, 398, and 400 are L-shaped when viewedfrom the bottom (FIG. 62), and support and position the back of theassembled cassettes 302 behind the pump cylinders 112 (FIG. 4) and aportion of the right side of the assembled cassettes 302 adjacent thepump cylinders 112. Note that the three right lateral support walls 390,392, and 394 and the three right corner support walls 396, 398, and 400together provide continuous support and positioning for the assembledcassettes 302 in the first, second, and third positions, respectively.

Located in the raised material forming the left lateral support wall 384near the back thereof is a threaded aperture 02. A single segment ofraised material forms the right lateral support wall 390, the rightcorner support wall 396, and the left lateral support wall 386; locatedin that segment of raised material near the back thereof is a threadedaperture 404 on the left side near the right lateral support wall 390,and a threaded aperture 406 on the right side near the left lateralsupport wall 386. Likewise, a single segment of raised material formsthe right lateral support wall 392, the right corner support wall 398,and the left lateral support wall 388; located in that segment of raisedmaterial near the back thereof is a threaded aperture 408 on the leftside near the right lateral support wall 392, and a threaded aperture410 on the right side near the left lateral support wall 388. Finally, asingle segment of raised material forms the right lateral support wall394 and the right corner support wall 400 near the back thereof is athreaded aperture 412 near the right lateral support wall 394.

Located in the segment of raised material forming the right lateralsupport wall 390, the right corner support wall 396, and the leftlateral support wall 386 near the corner where the right lateral supportwall 390 and the right corner support wall 396 meet is an aperture 414which extends through the pump chassis 370 from top to bottom. Locatedin the segment of raised material forming the right lateral support wall392, the right corner support wall 398, and the left lateral supportwall 388 near the corner where the right lateral support wall 392 andthe right corner support wall 398 meet is an aperture 416 which extendsthrough the pump chassis 370 from top to bottom. Located in the segmentof raised material forming the right lateral support wall 394 and theright corner support wall 400 near the corner where the right lateralsupport wall 394 and the right corner support wall 400 meet is anaperture 418 which extends through the pump chassis 370 from top tobottom.

Note that with the assembled cassettes 302 positioned and mounted in thefirst, second, and third positions, the aperture 414, the aperture 416,and the aperture 418, respectively, will be directly back of the pistonrods 292 of the assembled cassettes 302 (FIG. 46). The apertures 414,416, and 418 will be used to mount the drive shafts connected to thejaws assembles 360 (FIGS. 59 through 61) used to drive the pistonassembly 280.

Located between the left lateral support wall 384 and the right lateralsupport wall 390 is a longitudinal rectangular recess 420 in the bottomsurface of the pump chassis 370. Similarly, located between the leftlateral support wall 386 and the right lateral support wall 392 is alongitudinal rectangular recess 422 in the bottom surface of the pumpchassis 370. Finally, located between the left lateral support wall 384and the right lateral support wall 390 is a longitudinal rectangularrecess 424 in the bottom surface of the pump chassis 370. While therectangular recesses 420, 422, and 424 do not extend through the pumpchassis 370, oval aperture 426, 428, and 430 smaller than therectangular recesses 420, 422, and 424 are located in the rectangularrecesses 420, 422, and 424, respectively, and extend through to the topside of the pump chassis 370.

The rectangular recesses 420, 422, and 424 will be used to mount sensormodules therein, and the oval aperture 426, 428, and 430 are to allowthe wires from the sensor modules to extend through the pump chassis370. Note that with the assembled cassettes 302 positioned and mountedin the first, second, and third positions, the rear-most extending upperportions of the assembled cassettes 302 will be located over therectangular recesses 420, 422, and 424.

Located in front of the right corner support wall 396 is a circularrecess 432 in the bottom surface of the pump chassis 370. Similarly,located in front of the right corner support wall 398 is a circularrecess 434 in the bottom surface of the pump chassis 370. Finally,located in front of the right corner support wall 400 is a circularrecess 436 in the bottom surface of the pump chassis 370. While thecircular recesses 432, 434, and 436 do not extend through the pumpchassis 370, square apertures 438, 440, and 442 smaller than thecircular recesses 432, 434, and 436 are located in the circular recesses432, 434, and 436, respectively, and extend through to the top side ofthe pump chassis 370.

The circular recesses 432, 434, and 436 will be used to mount valveactuator guides therein, and the cylindrical aperture 450, 452, and 454are to allow valve actuators to extend through the pump chassis 370 andto orient the valve actuator guides. Note that with the assembledcassettes 302 positioned and mounted in the first, second, and thirdpositions, the circular recess 432, the circular recess 434, and thecircular recess 436, respectively, will correspond exactly with thelocations of the domed portions 178 of the valve diaphragms 170 in theassembled cassettes 302 (FIG. 43).

Located to the left of the circular recess 432 and in front of therectangular recess 420 is a circular recess 444 in the bottom surface ofthe pump chassis 370. Similarly, located to the left of the circularrecess 434 and in front of the rectangular recess 422 is a circularrecess 446 in the bottom surface of the pump chassis 370. Finally,located to the left of the circular recess 436 and in front of therectangular recess 424 is a circular recess 448 in the bottom surface ofthe pump chassis 370. While the circular recesses 444, 446, and 448 donot extend through the pump chassis 370, cylindrical apertures 450, 452,and 454 of a smaller diameter than the circular recesses 444, 446, and448 are located in the circular recesses 444, 446, and 448,respectively, and extend through to the top side of the pump chassis370.

The circular recesses 444, 446, and 448 will be used to mount pressuretransducers therein, and the cylindrical apertures 438, 440, and 442 areto allow wires from the pressure transducers to extend through the pumpchassis 370. Note that with the assembled cassettes 302 positioned andmounted in the first, second, and third positions, the circular recess444, the circular recess 446, and the circular recess 448, respectively,will correspond with the locations of the pressure diaphragms 182 of thevalve diaphragms 170 in the assembled cassettes 302 (FIG. 43).

Projecting from the surface on the top side of the pump chassis 370 area number of raised segments in which threaded apertures are located tosupport the drive assembly. A cylindrical raised segment 456 is locatedto the left of th cylindrical aperture 450 on the top side of the pumpchassis 370. A laterally extending oval raised segment 458 is locatedbetween the square aperture 438 and the cylindrical aperture 452 on thetop side of the pump chassis 370. A second laterally extending ovalraised segment 460 is located between the square aperture 440 and thecylindrical aperture 454 on the top side of the pump chassis 370. Acylindrical raised segment 462 is located to the right of the squareaperture 442 and is laterally aligned with the rear-most portions of theoval raised segments 458 and 460. Finally, a cylindrical raised segment464 is located to the right of the square aperture 442 and is laterallyaligned with the front-most portions of the oval raised segments 458 and460.

Located in the cylindrical raised segment 456 is a threaded aperture466. Located in the oval raised segment 458 is a threaded aperture 468near the rear-most portion of the oval raised segment 458, a threadedaperture 470 near the front-most portion of the oval raised segment 458,and a threaded aperture 472 centrally located in the oval raised segment458. Similarly, located in the oval raised segment 460 is a threadedaperture 474 near the rear-most portion of the oval raised segment 460,a threaded aperture 476 near the front-most portion of the oval raisedsegment 460, and a threaded aperture 478 centrally located in the ovalraised segment 460. Located in the cylindrical raised segment 462 is athreaded aperture 480. Finally, located in the cylindrical raisedsegment 464 is a threaded aperture 482.

The apertures 414, 416, and 418 through the pump chassis 370 terminatein raised segments extending from the top surface of the pump chassis370. A raised segment 484 is located around the opening of the aperture414 on top of the pump chassis 370, a raised segment 486 is locatedaround the opening of the aperture 416 on top of the pump chassis 370,and a raised segment 488 is located around the opening of the aperture418 on top of the pump chassis 370.

Extending upwardly from the raised segment 484 behind the aperture 414on the left side is a guide finger 490, and on the right side is a guidefinger 492. The guide fingers 490 and 492 are parallel and have a spacetherebetween. Extending upwardly from the raised segment 486 behind theaperture 416 on the left side is a guide finger 494, and on the rightside is a guide finger 496. The guide fingers 494 and 496 are paralleland have a space therebetween. Extending upwardly from the raisedsegment 488 behind the aperture 418 on the left side is a guide finger498, and on the right side is a guide finger 500. The guide fingers 498and 500 are parallel and have a space therebetween.

Referring now to FIGS. 66 through 69, a cassette guide 510 for use inguiding the installation of the assembled cassette 302 into the properlocation for latching on the pump chassis 370 is illustrated. Disposedto the rear of the cassette guide 510 at the right side is an aperture512, and at the left side is an aperture 514. The aperture 512 will bealigned with the threaded aperture 404 (FIG. 62), the threaded aperture408, or the threaded aperture 412 while the aperture 514 will be alignedwit the threaded aperture 402, the threaded aperture 406, or thethreaded aperture 410 to install the cassette guide 510 in either thefirst, second, or third position.

The top side (FIG. 66) of the cassette guide 510 has a rectangularrecess 516 therein, which rectangular recess 516 corresponds in size tothe rectangular recesses 420, 422, and 424 in the pump chassis 370. Thesensor modules will be accommodated between the rectangular recesses 516in the cassette guides 510 and the rectangular recesses 420, 422, and424 in the pump chassis 370. The right side of this rectangular recess516 is exposed through a rectangular aperture 518 on the bottom of thecassette guide 510 (FIG. 67).

An area 520 on the bottom of the cassette guide 510 immediately to thefront of the rectangular aperture 518 and an area 522 to the right andto the back of the rectangular aperture 518 is recessed upward from thebottom surface 524 of the cassette guide 510. At the front right cornerof the rectangular aperture 518 a square segment 528 extends downward tothe level of the bottom surface 524 of the cassette guide 510. Locatedimmediately forward of the square segment 528 is a thin rectangulartrack 530 extending from the right side of the cassette guide 510. Thethin rectangular track 530 terminates at the front end thereof in ablocking segment 532.

The front end of the cassette guide 510 has a rounded notch 534 therein,which rounded notch is positioned when the cassette guide 510 isinstalled on the pump chassis 370 to receive the outlet tube mountingcylinder 144 on the cassette body 100 (FIG. 4). When the cassette guide510 in installed on the pump chassis 370, the rear-most portion of theassembled cassette 302 will fit between the cassette guide 510 and thebottom of the pump chassis 370. Accordingly, the cassette guide 510together with the various support walls on the bottom of the pumpchassis 370 aids in the installation of the assembled cassettes 302 inthe proper position for latching.

Referring next to FIG. 70, a pump shaft 540 is illustrated which isessentially cylindrical. Near the top end of the pump shaft 540 on, thefront side thereof a cam follower wheel 542 is mounted for rotationabout a short axle 544 extending orthogonally from the pump shaft 540.On the front side of the pump shaft 540 at the same location analignment wheel 546 is mounted for rotation about a short axle 548extending orthogonally from the pump shaft 540 on the opposite side ofthe short axle 544. Near the bottom end of the pump shaft 540 on therear side thereof is a conical recess 550, which will be used to attachthe jaws assembly 360 (FIG. 59 through 61) to the pump shaft 540.

Referring next to FIGS. 71 through 76, a slide lock 560 which is formounting on the thin rectangular track 530 of the cassette guide 510(FIG. 67) is illustrated. The slide lock 560 has a U-shaped slidechannel 562 at the front thereof, with the open portion of the U facingleft and extending from front to rear. The right side of the slidechannel 562, which is the bottom of the U, has a rectangular notch 564located near the front thereof, which notch 564 runs from the top to thebottom of the slide channel 562.

Extending back from the rear of the slide channel 562 at the bottomthereof is a thin rectangular connecting segment 566, which effectivelyextends from the leg of the U at the bottom of the slide channels 562.Attached at the rear edge of the rectangular connecting segment 566 is aU-shaped channel 568 with the open portion of the U facing right andextending from top to bottom. The forward leg of the U of the U-shapedchannel 568 is attached to the rectangular connecting segment 566 at thetop of the U-shaped channel 568. It will be appreciated that the topsurface of the rectangular connecting segment 566 and the top of theU-shaped channel 568 (which is U-shaped) are coplanar, and that theinterior surface of the lowermost leg of the slide channel 562 is alsocoplanar.

The upper left edge of the U-shaped channel 568 has a bevel 570 locatedthereon, with the bevel 570 being best illustrated in FIG. 76. Thefunction of the bevel 570 is as a light reflector, and will becomeapparent later in conjunction with the discussion of the mechanism forlatching the assembled cassette 302.

Referring now to FIGS. 77 through 79, an essentially cylindrical powermodule cam 580 is illustrated. The power module cam 580 has an aperture582 therethrough for mounting the power module cam 580 on a shaft (notshown), which the aperture 582 is shown from the bottom in FIG. 79. Thepower module cam 580 has apertures 584 and 586 through which means forretaining the power module cam 580 in position on a shaft may beinstalled. Located near to the bottom of the power module cam 580 is agroove 588 located around the outer circumference of the power modulecam 580. The groove 588 will receive a drive belt which will drive thepower module cam 580 is a rotary fashion.

Located above and spaced slightly away from the groove 588 in the powermodule cam 580 is a retaining groove indicated generally at 590 formedin the surface of and extending around the circumference of the powermodule cam 580. The retaining groove 590 is of essentially uniform widthand depth in the surface of the power module cam 580, and varies indistance from the top side of the power module cam 580. As best seen inFIG. 77, the portion of the retaining groove 590 closest to the top ofthe power module cam 580 is disposed approximately one-hundredeightydegrees away from the portion of the retaining groove 590 furthest fromthe top of the power module cam 580. It will be noted that anon-rotating member having a portion thereof engaged in the retaininggroove 590 of the power module cam 580 will be driven in a reciprocatingfashion as the power module cam 580 is turned.

Located on the bottom of the power module cam 580 about the outerdiameter thereof is a cam surface indicated generally at 592. The camsurface 592 extends lower in one portion 593 than in the other portion595, as best shown again in FIG. 77. It will be apparent to thoseskilled in the art that one or more non-rotating member bearing on thecam surface 592 will be driven in reciprocating fashion as the powermodule cam 580 is turned.

The configurations of the retaining groove 590 and the cam surface 592are graphically illustrated in FIG. 80, which indicates how threemembers driven by the power module cam 580 are caused to operate as thepower module cam 580 is rotated through a three-hundred-sixty degreecycle. The retaining groove 590 is used to drive a pump member, whichdraws fluid in from a source to fill the pump chamber on an intakestroke, and pumps the fluid out on a pumping stroke. The cam surface 592is used to drive two valve members, namely an inlet valve and an outletvalve, which are driven by portions of the cam surface 592 which areseparated by approximately one-hundred-eighty degrees. It will at oncebe appreciated that the pump and valves being driven will be those ofthe assembled cassette 302.

The plot of pump displacement in FIG. 80 illustrates that there is afill cycle during which displacement increases from zero (or near zero)to full, and a pump cycle during which displacement decreases from fullto empty (or near empty). The retaining groove 590 has two flat portionswhich correspond to the flat portions of the pump displacement plot. Oneof the flat portions 594 is the portion of the retaining groove 590which is closest to the top thereof, and this flat portion 594corresponds to the zero displacement portion of the pump displacementplot. The other flat portion 596 is the portion of the retaining groove590 which is closest to the bottom thereof, and this flat portion 596corresponds to the full displacement portion of the pump displacementplot.

The portions of the retaining groove 590 which are located intermediatethe flat portions 594 and 596 are a positive portion 598 whichcorresponds to the increasing displacement portion of the pumpdisplacement plot, and a negative portion 600 which corresponds to thedecreasing displacement portion of the pump displacement plot. It shouldbe noted that the flat portions 594 and 596 are substantial enough toallow valve movement entirely during the flat portions of the pumpdisplacement plot. In the preferred embodiment, the flat portions 594and 596 each represent approximately sixty degrees of rotationalmovement, while the positive and negative portions 598 and 600 eachrepresent approximately one-hundred-twenty degrees of rotationalmovement.

The cam surface 592 of the power module cam 580 is described withreference to the inlet and outlet valve plots of FIG. 80. It will firstbe noted that the plots for the inlet and outlet valves are identical,but are located one-hundred-eighty degrees apart. As will become evidentlater in conjunction with the discussion of the valve actuators and thevalve actuator guide, the inlet and outlet valves are both driven by thecam surface 592, but by points on the cam surface which are locatedone-hundred-eighty degrees apart.

The lower portion 593 of the cam surface 592 corresponds to the closedpositions of both the inlet and outlet valves, while the higher portion595 of the cam surface 592 corresponds to the opened positions of boththe inlet and outlet valves. All valve movement is accomplished entirelyduring the periods in which pump displacement remains constant. In thepreferred embodiment where pump displacement is constant during twosixty degree periods and either increasing or decreasing during twoone-hundred-twenty degree periods, all valve movement is accomplishedduring the two sixty degree periods.

In addition, at least one valve is closed at any given time to preventfree flow through the assembled cassette 302. Therefore, it will beappreciated by those skilled in the art that the period during which theinlet and outlet valves transition between fully open and closedpositions will be limited to thirty degrees or less in the preferredembodiment. During each of the sixty degree periods during which pumpdisplacement is constant, the one of the valves which is open willclose, and only then will the other valve, which was closed, be allowedto open.

Moving next to FIG. 81, a drive module assembly 602 is illustrated whichincludes the power module cam 580 discussed above. The various partsdescribed in conjunction with FIG. 81 are mounted onto a drive modulechassis 604, which will in turn be mounted onto one of the three pumppositions on the top side of the pump chassis 370. As shown in FIG. 82,the drive module chassis 604 has an aperture 605 therethrough on theleft side thereof, and two apertures 607 and 609 therethrough on theright side thereof. The apertures 605, 607, and 609 are for use infastening the drive module assembly 602 to the pump chassis 370.

An ironless core DC motor 606 is used to drive the system. The motor 606typically has a built-in gear reduction unit to reduce the output speedof the motor 606. The end of the motor 606 having the output shaft (notshown) is mounted onto the top of the drive module chassis 604 at oneside thereof with the output shaft extending through the drive modulechassis 604. A drive pulley 608 is mounted on the output shaft and isdriven by the motor 606.

A one-way clutch 610 is mounted onto the top of the drive module chassis604 at the other side thereof. Such devices are commercially available,and are also referred to is DC roller clutches or overrunning clutches.The one-way clutch 610 supports a drive shaft 612 for rotation therein;both ends of the drive shaft 612 extend from the one-way clutch 610. Theone-way clutch 610 allows the drive shaft 612 to rotate in one directiononly; in the preferred embodiment, the rotation is clockwise when viewedfrom the top. The power module cam 580 is mounted on the bottom end ofthe drive shaft 612 extending from the one-way clutch 610. A drive belt613 is mounted over the drive pulley 608 and in the groove 588 in thepower module cam 580. The motor 606 will thereby drive the power modulecam 580 and the drive shaft 612.

Fixedly mounted above the one-way clutch 610 is an angular incrementalposition sensor 614. A sensor disk 616 is fixedly mounted on the top endof the drive shaft 612, and rotates with the drive shaft 612 and thepower module cam 580. The position sensor 614 is used to provide angularincremental and absolute position feedback for control of the drivemechanism and cassette. In the preferred embodiment, the position sensor614 should also be capable of direction sensing.

Referring next to FIGS. 85 through 87, a valve actuator 620 isillustrated which is driven by the power module cam 580 (FIGS. 77through 79). The valve actuator 620 includes a thin, essentiallyrectangular portion 622, and has a circular bearing 624 rotatablymounted near the top thereof. The circular outer diameter of the bearing624 extends slightly above the top of the rectangular portion 622. Thebearing 624 is the portion of the valve actuator 620 which will be incontact with the cam surface 592 of the power module cam 580.

The rectangular portion 622 of the valve actuator 620 has chamferededges on the lower end thereof as indicated generally at 625, and has asmall notch 626, 628 in both lateral sides of the rectangular portion622 at a location above the lower end thereof. The small notches 626 and628 are for receiving means for retaining the valve actuator 620 inposition once it is installed; this will become evident below inconjunction with the discussion of the assembly of the main pump unit.

Moving next to FIGS. 83 and 84, a valve actuator guide 630 isillustrated which is used to guide and retain in position pairs of thevalve actuators 620. The upper portion 632 of the valve actuator guide630 is square in cross-section, and lower portion 634 is circular incross-section. Extending vertically through both the square upperportion 632 and the circular lower portion 634 of the valve actuatorguide 630 are two apertures 636 and 638, which are rectangular incross-section. The apertures 636 and 638 are sized to allow therectangular portion 622 of the valve actuator 620 to slide freelytherein in each of the apertures 636 and 638.

One of the valve actuator guides 630 will be installed into each of thepump positions in the pump chassis 370. In the first pump position, thesquare upper portion 632 of the valve actuator guide 630 will be locatedin the square aperture 438 on the pump chassis 370 and the circularlower portion 634 of the valve actuator guide 630 will be located in thecircular recess 432 on the pump chassis 370. In the second pumpposition, the square upper portion 632 will be located in the squareaperture 440 and the circular lower portion 634 will be located in thecircular recess 434. In the third pump position, the square upperportion 632 will be located in the square aperture 442 and the circularlower portion 634 will be located in the circular recess 436.

Referring next to FIGS. 88 through 90, a pressure transducer 660 isillustrated. One of the pressure transducers 10 660 will be installed inthe pump chassis 370 in each pump position, in the circular recesses444, 446, and 448. The pressure transducer 660 is essentiallycylindrical, with a groove 662 located around the circumference of thepressure transducer 660. The groove 662 is to receive an elastomericO-ring, which will both retain the pressure transducers 660 in thecircular recesses 444, 446, and 448, and provide a fluid seal. Locatedon top of the pressure transducer 660 is a square segment 664 in whichis located the actual transducer, which square segment 664 will bereceived in the cylindrical apertures 450, 452, and 454. Extendingupward from the square segment 664 are several leads 666.

Referring next to FIGS. 91 through 96, an optical sensor module 670 isillustrated. The optical sensor module 670 is essentially rectangular incross-section, with a wider rectangular flange 672 on top of therectangular portion, and an oval portion 674 above the rectangularflange 672. A flex cable 676 extends from the top of the oval portion674. Located around the circumference of the oval portion 674 is agroove 678, which will receive an elastomeric O-ring, which will retainthe oval portion 674 of the optical sensor modules 670 in the ovalapertures 426, 428, or 430. The rectangular flange 672 of the opticalsensor modules 670 will fit into the rectangular recesses 420, 422, or424, in the first, second, or third pump positions, respectively.

The rectangular portion of the optical sensor module 670 has located inthe front thereof and immediately under the rectangular flange 672 anotch indicated generally by 680, which notch 680 will receive therearmost portion of the assembled cassette 302. The bottom of therectangular portion of the optical sensor module 670 has an opticallight source 682 and an optical light sensor 684 located thereon inlocations near and equidistant from the right side thereof. The opticallight source 682 and the optical light sensor 684 are used to detectwhen the slide lock 560 is in the closed position, as will be discussedbelow.

Located on the upper surface of the notch 680 in the optical sensormodule 670 are three optical light sources 686, 688, and 690, whichextend in a line from left to right on the upper surface of the notch680. Located immediately below the three optical light sources 686, 688,and 690 on the lower surface of the notch 680 in the optical sensormodule 670 near the right side thereof are three optical light sensors692, 694, and 696, which also extend in a line from left to right on thelower surface of the notch 680. The three optical light sources 686,688, and 690 and the three optical light sensors 692, 694, and 696 areused to provide the three cassette identification bits, as will bediscussed below.

Also located on the lower surface of the notch 680 in the optical sensormodule 670 toward the left side thereof is an optical light source 698.Located in front of the optical light source 698 is an optical lightsensor 700. The optical light source 698 and the optical light sensor700 are used to detect the presence (or absence) of an air bubble in thefluid line in the cassette. The location of the optical light source 698and the optical light sensor 700 as illustrated in FIG. 96 is that ofthe preferred embodiment, and operation of that preferred embodiment aswell as the configurations and operational descriptions of severalalternate embodiments are discussed below.

Referring next to FIGS. 97 and 98, a valve actuator seal 650 is shownwhich is used both to provide a fluid seal and, more importantly, toretain the valve actuators 620 (FIGS. 85 through 87) in an upwardposition with their bearings 624 against the lower portion 593 of thepower module cam 580. The outer circumference of the valve actuatorseals 650 is of a size allowing them to be retained in a friction fit inthe circular recesses 432, 434, and 436 below the valve actuator guides630. A metal ring (not shown) may be molded into the outer diameter ofthe valve actuator seals 650 to better enable them to be better retainedin the circular recesses 432, 434, and 436.

Two apertures 652 and 654, which are rectangular in configuration, arelocated in the valve actuator seal 650 to receive the bottom portions ofthe rectangular portion 622 of the valve actuator 620. The lengths ofthe apertures 652 and 654 are shorter than the width of the rectangularportion 622 of the valve actuator 620, with the small notches 626 and628 in the rectangular portion 622 being used to capture to ends of oneof the apertures 652 and 654. It will be appreciated that the smallnotches 626 and 628 of the valve actuators 620 will engage the apertures652 and 654 in the valve actuator seal 650, thereby allowing the valveactuator seal 650 to exert a bias on the valve actuators 620. As will beseen below, the bias exerted by the valve actuator seal 650 on the valveactuators 620 is an upward one, urging the valve actuators 620 againstthe lower portion 593 of the power module cam 580.

In the previous discussions of the various parts of the main pump unit,the function and interrelationship between parts has been brieflydiscussed. Before moving on to the operation of the main pump unit andthe assembled cassette 302, a brief discussion of the assembly of themain pump unit is in order. This discussion specifically refers to FIGS.62 through 65 (the pump chassis 370), FIG. 99, and FIG. 112, and also toother figures which are specifically mentioned in the discussion.

A pump shaft bearing 640 is installed in both the top and the bottom ofeach of the apertures 414, 416, and 418 in the pump chassis 370. Thepump shaft bearings 640 (FIG. 112) are essentially cylindrical and havea cylindrical aperture therethrough. In the preferred embodiment, theouter surface of the pump shaft bearings 640 have a raised portion orridge 641 near the top thereof and fit in the apertures 414, 416, and418 from the top and the bottom thereof in an interference fit to retainthem in the apertures 414, 416, and 418 in the pump chassis 370. Thepump shaft bearing 640 are preferably made of a low friction materialsuch as Teflon to allow the pump shafts 540 to move freely therein. Itwill also be appreciated that a single bearing could be used in each ofthe apertures 414, 416, and 418 in the pump chassis 370 which bearingwould extend all the way through the apertures 414, 416, and 418.

Next, the valve actuator guides 630 are installed from the bottom of thepump chassis 370 into the circular recess 432 and the square aperture438 in the first pump position, into the circular recess 434 and thesquare aperture 440 in the second pump position, and into the circularrecess 436 and the square aperture 442 in the third pump position. Withthe valve actuator guides 630 installed in the pump chassis 370 thebottom surface of the valve actuator guides 630 leaves a portion of thecircular recesses 432, 434, and 436 open from the bottom side of thepump chassis 370. The valve actuator seals 650 (FIGS. 97 and 98) will beinstalled later in the circular recesses 432, 434, and 436 below thevalve actuator guides 630.

The next step in the assembly is to install the two sensor modules. Thepressure transducers 660 (FIGS. 88 through 90) are installed from thebottom of the pump chassis 370 into the circular recesses 444, 446, and448. The pressure transducers 660 are essentially cylindrical, and withO-rings in the grooves 662 fit snugly into the circular recesses 444,446, and 448 with their bottom surfaces flush with the bottom surface ofthe pump chassis 370 around the circular recesses 444, 446, and 448; thetops of the cylindrical portion of the pressure transducers 660 fitagainst the cylindrical apertures 450, 452, and 454 in the pump chassis370. Not shown in the drawings is the preferred embodiment's use of athin membrane adhesively placed over the bottom of the pressuretransducer 660 and the portions of the bottom surface of the pumpchassis 370 thereabout. This thin membrane protects the pressuretransducer 660 from fluids which may inadvertently or accidentally endup on the device.

The optical sensor assembles 570 (FIGS. 91 through 96) are installed inthe rectangular recesses 420, 422, and 416 of the pump chassis 370, withthe oval portions 674 of the optical sensor modules 670 fitting into theoval apertures 426, 428, and 430. The optical sensor modules 670 areretained in position by the pressure of O-rings in the grooves 678 inthe optical sensor modules 670, and by the cassette guides 510.

The next step in the assembly of the main pump unit mechanicalcomponents onto the pump chassis 370 is the installation of the cassetteguide 510 (FIGS. 66 through 69)and the slide lock 560 (FIGS. 71 through76). The slide lock 560 is installed onto the cassette guide 510 byplacing the portion of the slide lock 560 including the bottom of theslide channel 562 into the rectangular aperture 518 in the cassetteguide 510 from the top, with the rectangular connecting segment 566 ofthe slide lock 560 extending over the portion of the area 522 in theback of the cassette guide 510. This aligns the interior of the U-shapedslide channel 562 on the slide lock 560 with the back end of the thinrectangular track 530 on the cassette guide 510. The slide lock 560 isthen moved forward with respect to the cassette guide 510, with theinterior of the slide channel 562 fitting over the thin rectangulartrack 530 until the blocking segment of the cassette guide 510 iscontacted by the slide lock 560.

The cassette guides 510 together with the slide locks 560 may then bemounted into the three pump positions on the pump chassis 370, whichalready contain the optical sensor module 670, using two screws (notshown). In the first pump position, a screw is placed through theaperture 514 in the cassette guide 510 into the threaded aperture 402 inthe pump chassis 370, and a second screw is placed through the aperture512 in the cassette guide 510 into the threaded aperture 404 in the pumpchassis 370. In the second pump position, a screw is placed through theaperture 514 in the cassette guide 510 into the threaded aperture 406 inthe pump chassis 370, and a second screw is placed through the aperture512 in the cassette guide 510 into the threaded aperture 408 in the pumpchassis 370. In the third pump position, a screw is placed through theaperture 514 in the cassette guide 510 into the threaded aperture 410 inthe pump chassis 370, and a second screw is placed through the aperture512 in the cassette guide 51° into the threaded aperture 412 in the pumpchassis 370. By way of example, the cassette guide 510 and the slidelock 560 are shown mounted in the first pump position in FIG. 99.

Next, the pump shafts 540 are installed in the pump shaft bearings 640,which have previously been installed in the apertures 414, 416, and 418.The end of the pump shafts 540 containing the conical recess 550 thereinare inserted through the pump shaft bearings 640 from the top, with thealignment wheel 546 being located between one of the three pairs ofguide fingers, namely the guide fingers 490 and 492 for the first pumpposition, the guide fingers 494 and 496 for the second pump position,and the guide fingers 494 and 496 for the third pump position. Forexample, the pump shaft 540 is shown installed in the first pumpposition in FIG. 112.

The valve actuators 620 are installed next, with one pair of the valveactuators 620 being installed in each pump position. The bottom ends ofthe valve actuators 620 having the chamfered edges 625 are insertedthrough the top sides of the valve actuator guides 630, with one pair ofthe valve actuators 620 being installed in each of the three valveactuator guides 630. The pair of valve actuators 620 are inserted intothe apertures 636 and 638 in the valve actuator guides 630 with thebearings 624 on each of the pair of the valve actuaters 620 facing awayfrom each other.

It will be appreciated that the rectangular portions 622 of the valveactuators 620 will extend downward through the apertures 636 and 638 inthe valve actuator guides 630. As stated above, valve actuator seals 650are used in each of the three pump positions, and are mounted from thebottom of the pump chassis 370 into the circular recesses 432, 434, and436 below the valve actuator guides 630. The outer circumference of thevalve actuator seals 650 causes them to be retained in a friction fit inthe circular recesses 432, 434, and 436.

The lower ends of the rectangular portions 622 of each pair of the valveactuators 620 extend downward through the apertures 652 and 654 in thevalve actuator seal 650. The small notches 626 and 628 in one of thevalve actuators 620 in each pair is retained in the aperture 652 in thevalve actuator seal 650, and the other one of the valve actuators 620 ineach pair is retained in the aperture 654. As shown in FIGS. 113 and114, the valve actuator seals 650 will tend to urge the valve actuators620 in an upward direction. In the preferred embodiment, the bottoms ofthe valve actuators 620 having the chamfered edges 625 will protrudesomewhat from the bottom surface of the pump chassis 370 around thecircular recesses 432, 434, and 436 even when the valve actuators 620are in their open position. For example, in their closed position theymay protrude approximately thirty thousands of an inch, and in theiropen position they may protrude seventy thousands of an inch.

This upward biasing of the valve actuator 620 is essential both to allowthe assembled cassettes 302 to be freely inserted, and to maintain thevalve actuators 620 in an upward position with their bearings 624against the lower portion 593 of the power module cam 580. The valveactuator seals 650 accordingly function both to provide a fluid seal andto bias the valve actuators 620 in the upward position described.

The next step in the assembly of the main pump unit is to install adrive module assembly 602 (FIG. 81) onto each of the three pumppositions on the pump chassis 370. In the first pump position, the drivemodule assembly 602 will be supported above the top of the pump chassis370 by the cylindrical raised segment 456 and the oval raised segment458. Three screws (not shown) will be used to secure the drive moduleassembly 602 in the first pump position, with a first screw being placedthrough the aperture 605 in the drive module chassis 604 into thethreaded aperture 466 in the pump chassis 370, a second screw beingplaced through the aperture 607 in the drive module chassis 604 into thethreaded aperture 468 in the pump chassis 370, and a third screw beingplaced through the aperture 609 in the drive module chassis 604 into thethreaded aperture 470 in the pump chassis 370. In the first pumpposition, the power module cam 580 is supported directly above thesquare aperture 438 in the pump chassis 370, and the valve actuatorguide 630 and the two valve actuators 620 located in the first pumpposition.

In the second pump position, the drive module assembly 602 will besupported above the top of the pump chassis 370 by the oval raisedsegment 458 and the oval raised segment 460. Three screws (not shown)will be used to secure the drive module assembly 602 in the second pumpposition, with a first screw being placed through the aperture 605 inthe drive module chassis 604 into the threaded aperture 472 in the pumpchassis 370, a second screw being placed through the aperture 607 in thedrive module chassis 604 into the threaded aperture 474 in the pumpchassis 370, and a third screw being placed through the aperture 609 inthe drive module chassis 604 into the threaded aperture 476 in the pumpchassis 370. In the second pump position, the power module cam 580 issupported directly above the square aperture 440 in the pump chassis370, and the valve actuator guide 630 and the two valve actuators 620located in the second pump position.

In the third pump position, the drive module assembly 602 will besupported above the top of the pump chassis 370 by the oval raisedsegment 460, the cylindrical raised segment 462, and the cylindricalraised segment 464. Three screws (not shown) will be used to secure thedrive module assembly 602 in the third pump position, with a first screwbeing placed through the aperture 605 in the drive module chassis 604into the threaded aperture 478 in the pump chassis 370, a second screwbeing placed through the aperture 607 in the drive module chassis 604into the threaded aperture 480 in the pump chassis 370, and a thirdscrew being placed through the aperture 609 in the drive module chassis604 into the threaded aperture 482 in the pump chassis 370. In the thirdpump position, the power module cam 580 is supported directly above thesquare aperture 442 in the pump chassis 370, and the valve actuatorguide 630 and the two valve actuators 620 located in the third pumpposition.

The final component to be installed is the jaws assembly 360 (FIGS. 59through 61), with one jaws assembly 360 being installed in each of thethree pump positions onto the bottom of the pump shafts 540, which areinstalled in the apertures 414, 416, and 4-8. The bottom end of the pumpshaft 540 having the conical recess 550 therein is inserted into thecylindrical aperture 316 in the latch head 310 of the jaws assembly 360.A retaining screw (not shown) is screwed into the threaded aperture 31Bin the latch head 510, and into the conical recess 550 of the lo pumpshaft 540 to retain the jaws assembly 360 in place on the bottom of thepump chassis 370.

The location of the installed jaws assembly 360 is shown in FIG. 99,with the slide lock 560 and the latch jaw 340 in the open position. Thelink pin 354 on the latch jaw 340 is located in the U-shaped channel 568of the slide lock 560, and movement of the slide lock 560 willaccordingly cause the latch jaw 340 to move. When the slide lock 560 isfully forward, as shown in FIG. 99, the latch jaw 340 will be in theopen position, with the jaw portion 342 of the latch jaw 340 away fromthe right jaw 314 of the latch head 310. When the slide lock 560 ispushed toward the back of the pump chassis 370, as shown in FIG. 100,the latch jaw 340 will be in the closed position, with the jaw portion342 of the latch jaw 340 closely adjacent the right jaw 314 of the latchhead 310.

This completes the discussion of the assembly of the main pump unit withthree pump positions. It will, of course, be appreciated that the mainpump unit may be constructed with different numbers of pump positionswithout departing from the teachings herein. It is now appropriate todiscuss the installation of the assembled cassette 302 into the firstpump position, which is the subject of the above-identified applicationentitled "Cassette Loading and Latching Apparatus for a MedicationInfusion System," and the operation of the device to pump fluid and toperform the other associated functions. The operations of the other twopump positions are identical to the operation of the first pump positiondescribed below.

With the slide latch 240 pulled back fully away from the front of theassembled cassette 302 (FIGS. 43 through 48), the wider portion of theelongated, tear-shaped aperture 258 in the slide latch 240 will closethe outlet tube 306, preventing fluid from flowing through the assembledcassette 302. The inlet tube 304 is connected to a fluid source such asan IV bag (not shown), and the outlet tube 306 is connected to a fluiddelivery device such as an injection set (not shown), the use of whichis well known in the art. The slide latch 240 is opened, together withany other closures in the IV bag line, and fluid fills the lines, theassembled cassette 302, and the injection set. By tapping or shaking theassembled cassette 302 any residual air bubbles will flow out throughthe line. The slide latch 240 is then pulled back and the outlet tube306 is closed, and the system is in a primed condition with theassembled cassette 302 ready to be installed onto the main pump unit.

When the slide latch 240 is pulled back, an opening is left between thefront portion 242 of the slide latch 240 and the front top portion ofthe assembled cassette 302 (made up of the cassette body 100 and theretainer cap 190) facing the front portion 242 of the slide latch 240.By way of the example used herein where the assembled cassette 302 is tobe mounted in the first position (the position on the left end of thepump chassis 370), the opening between the front portion 242 of theslide latch 240 and the front top portion of the assembled cassette 302will admit the first pair of angled segments 372 and 374 as theassembled cassette 302 is installed. The top surface of the assembledcassette 302, which is the retainer cap 190 (FIG. 43), will mountagainst the bottom of the pump chassis 370 (FIG. 62).

Prior to installing the assembled cassette 30 into the main pump unit,the slide lock 560 must be fully forward with the latch jaw 340 openedaway from the latch head 310, as mentioned previously and as shown inFIG. 99. In addition, the jaws assembly 360 should be in its fullyupward position, which may be achieved by using the motor 606 to drivethe power module cam 580 to cause the jaws assembly 360 to be driven tothis position using the position sensor 614.

With the rear-most edge of the assembled cassette 302 tilted upward, therear-most edge of the top of the assembled cassette 302 is then placedagainst the bottom of the pump chassis 370 between the pressuretransducer 660 (mounted flush with the bottom of the pump chassis 370)and the top side of the cassette guide 510. The rear-most portion of thetop of the assembled cassette 302 is slid toward the back of the pumpchassis 370 into position between the left lateral support wall 384 onthe left side thereof and the right lateral support walls 390 on theright side thereof, with most of the rear-most portion of the top of theassembled cassette 302 fitting into the notch 680 in the optical sensormodule 670. The upper right back corner of the assembled cassette 302 issupported and positioned in the back of the assembled cassette 302behind the pump cylinder 112 (FIG. 4) and on the portion of the rightside of the assembled cassette 302 adjacent the pump cylinder 112 by theright corner support wall 396.

When the assembled cassette 302 is pushed fully back in place, the frontof the assembled cassette 302 is tilted upward against the bottom of thepump chassis 370, with the first pair of angled segments 372 and 374 onthe bottom of the pump chassis 370 fitting into the area between thefront portion 242 of the slide latch 240 and the front top portion ofthe assembled cassette 302. The slide latch 240 may then be pushed intothe cassette body 100, sliding the inverted L-shaped portion 250 of theslide latch 240 into engagement with the angled segment 372, and slidingthe inverted, backwards L-shaped portion 252 of the slide latch 240 intoengagement with the angled segment 374. The assembled cassette 302 willthus be held in position on the bottom of the pump chassis 370 until theslide latch 240 is again pulled back, releasing the assembled cassette302.

Simultaneously, the outlet tube 306 will be opened, but fluid will notflow through the outlet tube 306 since at least one of the valveactuators 620 will be in its fully downward position at any given time,thereby preventing free flow through the assembled cassette 302 wheneverthe assembled cassette 302 is installed on the main pump unit. It willalso be noted that in this initially installed position, the piston capportion 262 is located at the very top of the pump cylinder 112.

It will be appreciated as discussed above that the power module cam 580will operate both the reciprocations of the piston assembly 280 and themovement of the valve actuators 620A and 620B (FIG. 112). This pistonand valve drive system is the subject of the above-identifiedapplication entitled "Mechanical Drive System for a Medication InfusionSystem." The movement of the piston assembly 280 and the valve actuators620A and 620B will correspond to the charts of FIG. 80, with theinitially installed position corresponding roughly to the zero degreeposition of the charts. In this position, both the inlet valve actuator620A and the outlet valve actuator 620B are in their closed positions.

Note that the open positions of the inlet valve actuator 620A and theoutlet valve actuator 620B are their fully upward positions, and thattheir closed positions are their fully downward positions. Without theinlet valve actuator 620A and the outlet valve actuator 620B in place onthe domed portion 178 of the valve diaphragm 170 of the assembledcassette 302, the area including the first passageway 128, the smallerdiameter aperture 118 to the pump cylinder 112, and the secondpassageway 134 is entirely open and fluid flow therein is unrestricted.When the inlet valve actuator 620A is in its closed or fully downwardposition, the portion of the domed portion 178 located intermediate thefirst passageway 128 and the smaller diameter aperture 118 is forceddown onto the portion of the slightly raised border 146 between thefirst passageway 128 and the smaller diameter aperture 118, therebypreventing fluid flow between the first passageway 128 and the smallerdiameter aperture 110. This position of the inlet valve actuator 620A isreferred to as its closed position.

Similarly, when the outlet valve actuator 620B is in its closed or fullydownward position, the portion of the domed portion 170 locatedintermediate the smaller diameter aperture 118 and the second passageway134 is forced down onto the portion of the slightly raised border 146between the smaller diameter aperture 118 and the second passageway 134,thereby preventing fluid flow between the smaller diameter aperture 118and the second passageway 134. This position of the outlet valveactuator 620B is referred to as its open position.

The motor 606 will begin to drive the power module cam 580, causing theinlet valve actuator 620A to open, with the outlet valve actuator 620Bremaining closed, as shown in FIG. 113. As the power module cam 580continues to be turned by the motor 606, the piston cap portion 262 willbe drawn downward in the pump cylinder 112, causing fluid to be drawninto the pump cylinder 112 from the fluid source (not shown) through theinlet tube 304, the bubble trap 104, and the first passageway 128. Whenthe pump cylinder 112 is filled, the inlet valve actuator 620A isclosed. Only after the inlet valve actuator 620A is fully closed willthe outlet valve actuator 620B be opened. FIG. 114 shows the system withthe outlet valve actuator 620B opened, prior to any fluid being pumpedout. The main pump unit responds to an electronic control system (notshown) which operates the system. This electronic control system, whichis preferably microprocessor-based, may be either conventional as knownin the art, or it may differ to enhance the unique mechanical design ofthe system discussed herein.

Fluid will be pumped by the motor 606 turning the power module cam 580to drive the piston cap portion 262 upward in the cylinder, forcingfluid out of the pump cylinder 112, and eventually out of the assembledcassette 302 through the outlet tube 306, from which it is supplied tothe patient through the injection set (not shown). It will beappreciated by those skilled in the art that the system may pump fluidat any rate chosen, by operating the motor 606 to pump fluid. Inaddition, the use of the position sensor 614 will provide a feedbacksignal indicating the exact position of the power module cam 580 and thepiston assembly 280, thereby indicating how much fluid has been pumpedby the device.

As noted previously, the rear-most portion of the assembled cassette 302is located in the notch 680 of the optical sensor module 670 when thecassette is installed in the main pump unit. This is illustrated inFIGS. 101 and 102, which illustrate only the assembled cassette 302 andthe optical sensor module 670. In some situations it may be desirable touse several different types of assembled cassettes 302 with the systemdescribed herein. For example, different cassettes may require differentstroke volumes to provide different flow ranges, or require differentfittings on the inlet tube 304 and/or the outlet tube 306 of thecassettes. Special application cassettes such as enteral pump cassettes,continuous arterio-venous hemofiltration (CAVH) cassettes, continuousblood sampling cassettes, or autotransfusion cassettes may bemanufactured.

The use of the wrong cassette may present a high degree of danger, so itwill be perceived that it is highly desirable to identify the particularcassette installed. This may be accomplished by the use of the threecassette identifying indicia 148, 150, and 152. By making each of theseindicia a binary bit, up to eight different codes may be generated. Byusing redundant coding to ensure fail-safe operation, three differentcassettes can be identified. In addition, the absence of a cassette canalso be detected. In the example illustrated in the drawings, the firstcassette identifying indicia 148 and the third cassette identifyingindicia 152 are of a first type (identified as a logical one forconvenience), and the second cassette identifying indicia 150 is of asecond type (identified as a logical zero for convenience).

With the assembled cassette 302 installed with its rear-most portionlocated in the notch 680 of the optical sensor module 670, the firstcassette identifying indicia 148 is aligned with the first pair ofsensor elements, namely the optical light source 686 and the opticallight sensor 692. Similarly, the second cassette identifying indicia 150is aligned with the second pair of sensor elements, namely the opticallight source 688 and the optical light sensor 694. Likewise, the thirdcassette identifying indicia 152 is aligned with the third pair ofsensor elements, namely the optical light source 690 and the opticallight sensor 696.

The second cassette identifying indicia 150 (the logical zero) and thesecond pair of sensor elements are shown in FIG. 103. Light from theoptical light source 688 shines through the aperture 208 in the retainercap 190, and onto the cassette body 100, where it is dispersed by thesecond cassette identifying indicia 150, which comprises an inverted Vmolded into the bottom of the upper surface 102 of the cassette body100. Note that various prism types of construction could also be used todisperse the light, which does not reach the optical light sensor 694,resulting in a logical zero being output by the optical light sensor694. For example, the inverted V could be molded into the top side ofthe upper surface 102 of the cassette body 100. Other alternativesinclude using paint or other physical blocking expedients instead of adispersing lens, or selectively molding or not molding one or more ofthe apertures 206, 208, and 210 in the retainer cap 190 (FIGS. 13 and14).

The third cassette identifying indicia 152 (the logical one, like thefirst cassette identifying indicia 148, which is not shown here) and thethird pair of sensor elements are shown in FIG. 104. Light from theoptical light source 690 shines through the aperture 210 in the retainercap 190, and onto the third cassette identifying indicia 152 on thecassette body 100. The third cassette identifying indicia 152 is acylindrical projection extending up from the upper surface 102 of thecassette body 100, which cylindrical projection acts like a light pipeto conduct the light to the optical light sensor 696, where it causesthe optical light sensor 696 to generate a logical one output. Note thatin the preferred embodiment, the cassette body 100 is constructed ofclear plastic to allow the first cassette identifying indicia 148 andthe third cassette identifying indicia 152 to conduct lighttherethrough. Also in the preferred embodiment, when there is nocassette 302 in place, all three outputs are logical ones, and thissignal is used to indicate that no cassette has been installed or thatthe cassette 302 is improperly installed.

It will therefore be appreciated that the use of the three cassetteidentifying indicia 148, 150, and 152 allows the generation of threedigital cassette identifying signals which are supplied from the opticalsensor module 670 to the microprocessor (not shown) to identify theparticular type of cassette which is installed. By using this cassetteidentifying system, inappropriate use of an installed cassette and/orimproper cassette installation may be prevented.

It is desirable to provide an indication that the assembled cassette 302has been properly installed on the main pump unit, with the latchingmechanism properly closed. This occurs when the slide lock 560 is pushedfully back against the rear of the cassette guide 510. This isaccomplished by sliding the slide latch 240 fully into the assembledcassette 302, with the tab 257 on the slide latch 240 fitting into thenotch 564 on the slide lock 560 to drive the slide lock 560 back,thereby also latching the jaws assembly 360 onto the piston assembly280.

An indication of latching is provided through use of the optical lightsource 682 and the optical light sensor 684 on the bottom of the opticalsensor module 670. When the slide lock 560 is in its loading or forwardposition shown in FIG. 99, the bevel 570 on the optical sensor module670 is adjacent the optical light source 682 and the optical lightsensor 684 on the bottom of the optical sensor module 670, as shown inFIGS. 105 and 106. The presence of the bevel 570 reflects the lightcoming from the optical light source 682 to the right, away from theoptical light sensor 684, thereby preventing a latch closed signal. Whenthe slide lock 560 is pushed fully back to its closed or rear-mostposition shown in FIG. 100, the bevel 570 on the optical sensor module670 is not adjacent the optical light source 682 and the optical lightsensor 684 on the bottom of the optical sensor module 670, as seen inFIG. 107. Rather, a reflective surface 567 installed on the flat bottomof the rectangular connecting segment 566 of the slide lock 560 reflectslight from the optical light source 682 into the optical light sensor684, thereby generating a latch closed signal. The reflective surface567 acts as a mirror, and may be a foil segment which is, for example,hot stamped into the rectangular connecting segment 566 or adhesivelysecured to the bottom of the rectangular connecting segment 566.

Additional confirmation that the slide lock 560 was closed with anassembled cassette 302 in place may be obtained by verifying thecassette identifying indicia, as described above. In order to result inan absolutely positive confirmation that a cassette is properlyinstalled and that the slide lock 56 is in the closed position, thepreferred embodiment will require correct signals from both the opticallight sensor 684, and from the optical light sensors 692, 694, and 696.

One of the essential functions of the system is to enable the detectionof air in the fluid line of the system. The air-in-line detection (AILD)system of the preferred embodiment is shown in FIG. 108, and includesthe recessed lens portion 138 in the assembled cassette 302, and a pairof sensor elements, namely the optical light source 698 and the opticallight sensor 700 in the optical sensor module 670. The recessed lensportion 138 is an optical viewing area in the fluid pathway through theassembled cassette 302, and in the preferred embodiment shown in FIG.108 is an inverted prism. The recessed lens portion 138 in anyembodiment also includes a focusing lens, indicated generally at 697.The optical light source 698 and the optical light sensor 700 are bothmounted in the optical sensor module 670 below the recessed prismaticlens portion 138 in th installed cassette 302.

The optics of the system of FIG. 108 makes use of the properties oflight as it moves from one media to a less dense media, and is a"reverse reflected" configuration. When air is in the fluid channel, thelight from the optical light source 698 follows the path shown in FIG.108, reflecting off of one bottom side of the recessed prismatic lensportion 138 onto th other, and thence downward to the optical lightsensor 700. Even if the upper surfaces of the recessed prismatic lensportion 138 are wetted with a fluid film, total internal reflectionstill occurs. When fluid is in the channel, the light refracts throughthe recessed prismatic lens portion -38 into the fluid. If the fluid isclear, the light passes through the liquid to 170, where it is eitherabsorbed by the valve diaphragm 170 or the retainer cap 190, or passesthrough both the valve diaphragm 170 and the retainer cap 190.Accordingly, the valve diaphragm 170 may be clear, absorptive of light,or may scatter the light, not returning enough light to the opticallight sensor 700 to generate a signal indicative of air being in thefluid path. If the valve diaphragm 170 is clear, then the retainer cap190 may be clear, absorptive of light, or may scatter the light, againnot returning enough light to the optical light sensor 700 to generate asignal indicative of air being in the fluid path. If the fluid isopaque, the light is absorbed by the fluid. In any event, the light doesnot return to the photodetector. What little reflection of light mayoccur will be small compared to the air case.

Material requirements of the preferred embodiment shown in FIG. 108 arethat the cassette body 100 be made of clear material, that the valvediaphragm 170 be made of material which is clear, absorptive to light,or effectively scatters light. If the valve diaphragm 170 is clear, theretainer cap 190 must then be made of material which is clear,absorptive to light, or effectively scatters light. In summary, thefluid channel in the assembled cassette 302 is designed so that with thepresence of air in the fluid channel, light sent by the optical lightsource 698 will be detected by the optical light sensor 700. With fluidcontained in the fluid channel, little or no light will be detected,irrespective of the clarity or opaqueness of the fluid. It willtherefore be appreciated by those skilled in the art that air bubbles inthe line may be easily detected with the apparatus discussed above.

There are three alternate embodiments to the arrangement illustrated inFIG. 108. First, in FIG. 109, a reflective surface 702 is installed onthe side of the notch 680 in the optical sensor module 670 opposite theoptical light source 698 and the optical light sensor 700. The recessedlens portion 138 in this embodiment is V-shaped, with light beingdirected from the bottom of the V. The materials of the cassette body100, the valve diaphragm 170, and the retainer cap 190 are all clear.When a clear fluid is contained in the fluid pathway, light from theoptical light source 698 will refract through to the reflective surface702, and return to the optical light sensor 700, giving a high signal.When air is present in the fluid pathway, the light from the opticallight source 698 will reflect off of the recessed lens portion 130without passing therethrough, thereby not reaching the optical lightsensor 700. However, when lipids are contained in the fluid pathway, thelight will refract through the recessed lens portion 138 and be absorbedby the lipids, giving a signal indicative of air in the fluid pathway.It will thereby be appreciated that the arrangement shown in FIG. 109 issuitable for use with clear fluids only.

Referring next to FIG. 110, a further variation is illustrated whichuses a V-shaped channel, with the bottom of the V being flat. Light isdirected from the optical light source 698, which is mounted on the topof the notch 680 in the optical sensor module 670, directly opposite theoptical light sensor 700 on the bottom of the notch 680 in the opticalsensor module 670. The materials of the cassette body 100, the valvediaphragm 170, and the retainer cap 190 are again clear. It will at oncebe appreciated that the signal received by the optical light sensor 700will be low for lipids in the fluid pathway, and high for clear fluidsin the fluid pathway. When air is present in the fluid pathway, some ofthe light will reflect off of the sides of the V, not reaching theoptical light sensor 700, while some of the light will pass through theflat bottom of the V, reaching the optical light sensor 700. Therefore,for air a medium level signal will be received. The system of FIG. 110is accordingly a three level system, and not digital.

Referring next to Figure a third variation is illustrated which uses aV-shaped recessed lens portion 138, with light being directed from thetop of the V. In this embodiment, the optical light source 698 and theoptical light sensor 700 are mounted on the top of the notch 680 in theoptical sensor module 670, rather than on the bottom. The materials ofthe cassette body 100, the valve diaphragm 170, and the retainer cap 190are again all clear. The signal received by the optical light sensor 700will be high with air in the fluid pathway, low with clear liquids inthe fluid pathway, and generally medium with lipids contained in thefluid pathway. The system of FIG. 111 is a three level system like thesystem of FIG. 110, but the optics of the system of FIG. 110 aresuperior to the optics of the system of FIG. 111.

Referring next to FIGS. 115 and 116, the operation of the pressuretransducer system, which provides the signal used by the presentinvention, may be discussed. As may be seen, the pressure diaphragm 182contacts the bottom of the pressure transducer 660, which is flat.Additionally, the pressure diaphragm 182 does not contact the pressureplateau 130 either on the top or on the sides thereof, making themovement of the pressure diaphragm 182 highly accurate and sensitive.

The pressure transducer 660 has a thin stainless steel diaphragm 710 atthe bottom thereof. The diaphragm 710 is supported from the edges by astainless steel housing 712, which housing 712 contains therein apassageway 714 leading to the square segment 664. The square segment 664contains a sensor element (not shown in detail) communicating with thepassageway 714, which sensor element is a standard siliconpiezoresistive wheatstone bridge type device 716. The passageway 714 isfilled with silicone oil to communicate pressure on the diaphragm 710 tothe silicon piezoresistive wheatstone bridge type device 716.

It will be appreciated by those skilled in the art that the outlet sidefluid pressure within the assembled cassette 302 will be communicatedthrough the pressure diaphragm 182 and the diaphragm 710 to the siliconeoil in the passageway 714, and thereby to the silicon piezoresistivewheatstone bridge type device 716, which provides an electricalindication of pressure on the leads 666. Accordingly, pressure may bemeasured to provide an indication of downstream occlusion, pumping,fluid pressure, etc.

Referring now to FIG. 117, the standard silicon piezoresistivewheatstone bridge type device 716 of pressure transducer 660 is shown inelectrical schematic fashion inside the dotted lines. The four leads666, unnumbered in FIG. 117, are shown exiting the standard siliconpiezoresistive wheatstone bridge type device 716. A five volt powersupply (not shown) is used to power the circuit of FIG. 117. The fivevolt power supply is connected through a switch 750 to supply thestandard silicon piezoresistive wheatstone bridge type device 716, theother side of which is grounded. The other two leads from the standardsilicon piezoresistive wheatstone bridge type device 716 provide theelectrical signal indicative of pressure sensed in the patient side ofthe cassette.

These two leads from the standard silicon piezoresistive wheatstonebridge type device 716 are supplied to an amplifier 752, which amplifiesthe signal by a factor K. The amplifier 752 also has a zero offsetadjustment, and is powered by the five volt power supply through theswitch 750. The amplified signal from the amplifier 752 is supplied toan analog filter 754, which is a low pass filter such as a first orderswitching capacitor filter. It should be explained that the switch 750is strobed to minimize power consumption, for example at a rate of 46.5Hz in the preferred embodiment. This rate was chosen as the slowestsampling rate sufficiently fast to meet the Shannon sampling criteriawhile subject to arterial waveforms during an arterial infusion. Theanalog filter 754 eliminates the harmonics introduced by power strobingwith the switch 750, and also attenuates hydraulic noise which couldotherwise cause false occlusion alarms. A typical value for τ₁ in theLaplace transform 1/(sτ₁ +1) of the analog filter 754 is 0.44 seconds.

The output from the analog filter 754 is supplied to a sampler 756,shown schematically as a switch. The period T for the sampler 756 maybe, for example, 0.18 second, or a sampling frequency f_(s) of 5.6 Hz.The sampling rate is selected to be the largest interval stillexhibiting a reasonable amount of overshoot and undershoot in thepredicted pressure signal, which will be discussed further below. Theoutput of the sampler 756 is supplied to an eight-bit quantizer 758,which is supplied with power directly from the five volt power supply.The eight-bit quantizer 758 in conjunction with the sampler 756 acts asan analog-to-digital converter, and the output of the eight-bitquantizer 758 is a digital pressure signal P_(k).

The digital pressure signal P_(k) is supplied to a differentiator 760.The differentiator 760 takes the first difference, which may berepresented using the Z transform transfer function 1-z⁻¹. The output ofthe differentiator 760 is a digital pressure rate change signal P_(k).The digital pressure signal Pk and the digital pressure rate changesignal P_(k) are supplied by the circuit of FIG. 117 as inputs to themicroprocessor, the relevant portions of which for the present inventionare shown in FIG. 118.

It will be seen from FIG. 118 that there are three branches provided asinputs to an OR gate 762, the logical one output of which OR gate 762will cause an occlusion alarm to be given. It is therefore the case thatif any one of the three branches of FIG. 118 results in a logical onebeing supplied to the OR gate 762, an alarm indicating the existence ofa patient-side occlusion will be given.

As mentioned previously, the infusion system described herein and in theabove-identified applications is capable of being configured as a numberof different systems. For the occlusion detector of the presentinvention, there are two alternatives: either the system is configuredas a flow controller, or it is configured as another type of pump. Thisdifference is caused by the fact that fluid pressure in a flowcontrolled is typically substantially less than fluid pressure of any ofthe other configured systems.

The left-most branch of the circuit of FIG. 118 is applicable to eitherof the two basic types of systems, with one difference which will becomeevident below, for situations in which the digital pressure change rateP_(k) is greater than or equal to five pounds per square inch per second(PSI/sec). Both the digital pressure signal P_(k) and the digitalpressure rate change signal P_(k) are supplied to a one-step aheadpredictor 764. One step is equal to the time period T, or 0.18 seconds,so the one-step ahead predictor 764 is used to calculate what thedigital pressure signal P_(k) will be in 0.18 seconds after the presenttime. The one-step ahead predictor 764 uses the formula P_(k+1) =(τ₁+T)*P_(k) +P_(k) to compute a value for the predicted pressure signalP_(k+1), where τ₁ is the time constant of the analog filter 754, and Tis the time constant of the sampler 756.

This predicted pressure signal P_(k+1) is supplied to a first alarmthreshold device 766, which has a logical one output when the predictedpressure signal P_(k+1) reaches or exceeds a preselected value. Thispreselected value is typically six PSI if the system is configured as aflow controller, or fifteen PSI if the system is configured as one ofthe other types of infusion pumps. The output of the first alarmthreshold device 766 is supplied to the OR gate 762, and if it is alogical one, an alarm is sounded.

The other two branches are utilized if the digital pressure change ratesignal P_(k) is less than five PSI/sec. If the digital pressure changerate signal P_(k) is less than five PSI/sec and the system is configuredas a flow controller, the middle branch of FIG. 118 is utilized. If thedigital pressure change rate signal P_(k) is less than five PSI/sec andthe system is configured as one of the other types of pumps, the rightbranch of FIG. 118 is utilized.

The middle branch, used when the digital pressure change rate signalP_(k) is less than five PSI and the system is configured as a flowcontroller, uses what is termed the absolute method. Note that eitherone or the other of the middle and right branches will be used, with theother disconnected from the system and having a logical zero outputsupplied therefrom to the OR gate 762. The digital pressure signal P_(k)is supplied as an input to a digital filter 768, which typically afirst-order low-pass filter. In the preferred embodiment, the unity gaindigital filter 768 uses a Z transform transfer function of b/(1-a*z⁻¹),with a typical time constant of 2.4 seconds, or a cutoff frequency of0.067 Hz. The coefficients a and b determine the gain and the cutofffrequency.

The output of the digital filter 768 is the digitally filtered digitalpressure signal P_(f),k, which is supplied as an input to a second alarmthreshold device 770. The second alarm threshold device 770 has alogical one output when the digitally filtered digital pressure signalP_(f),k reaches a preselected value. This preselected pressure value istypically set between one and one-half and six feet of water, with atypical default pressure value of three feet of water. The output of thesecond alarm threshold device 770 is supplied to the OR gate 762, and ifit is a logical one, an alarm is sounded.

The right branch, used when the digital pressure change rate signalP_(k) is less than five PSI/sec and the system is configured as a deviceother than a flow controller, uses what is termed the baseline method.The digital pressure signal P_(k) is supplied as an input to a thirdalarm threshold device 772, which uses the digital pressure signal P_(k)to determine a baseline pressure P_(b) for the system whenever infusionis commenced or when a new infusion rate takes effect.

The third alarm threshold device 772 calculates the baseline pressureP_(B) during the period from the beginning of the second stroke of thepump as driven by the motor 606 and as monitored by the angularincremental position sensor 614. For a new infusion operation, thiswould be triggered by the beginning of the second stroke. For a changedinfusion rate, it would be triggered by the beginning of the secondstroke at the new infusion rate. The first stroke is not used sinceinfusion startup may have a different pressure after the first stroke.

The third alarm threshold device 772 monitors the digital pressuresignal P_(k) from the start of the second stroke to the beginning of thethird stroke, and averages this pressure to produce the baselinepressure P_(B). The value of the baseline pressure P_(B) remainsconstant as long as the pump is being driven at the rate at which thebaseline pressure P_(B) was measured. A value for delta pressure ΔP issupplied to the third alarm threshold device 772, which value depends onthe type of pump configured. This delta pressure ΔP, when added to thebaseline pressure P_(B), yields an alarm threshold pressure P_(b),which, when reached, results in a logical one being output from thethird alarm threshold device 772. The output of the second alarmthreshold device 770 is supplied to the OR gate 762, and if it is alogical one, an alarm is sounded.

It is therefore apparent that when a digital pressure signal P_(k)reaches a value equal to the baseline pressure P_(b) plus the deltapressure ΔP, the alarm will be triggered. The value of the deltapressure ΔP for a neonatal pump configuration is quite low, as, forexample, one PSI. The value of the delta pressure ΔP for a generalpurpose or home health care pump configuration is an intermediate value,as, for example, five PSI. The value of the delta pressure ΔP for anoperating room pump is fairly high, as, for example, ten PSI.

In addition, the third alarm threshold device 772 will not allow thedigital pressure signal P_(k) to go beyond a predetermined maximum valuewithout initiating an alarm. Typically this maximum value is fifteenPSI. In this case, for example, if the baseline pressure P_(b) was sixPSI, and the delta pressure ΔP was ten PSI, for a total of sixteen PSI,an alarm would be sounded when the digital pressure signal P_(k) reachedfifteen PSI, even though this is below the calculated maximum of sixteenPSI.

It may thus be perceived by those skilled in the art that the presentinvention provides an alarm in the event of an occlusion in the fluidpath downstream of the pump in the disposable cassette. The system isintegrally contained in the disposable cassette/main pump unitcombination, provides a number of advantages, and enhances the operatingsafety of the overall system. The patient-side occlusion detectionsystem of the present invention responds quickly to "rapid occlusions"such as those caused by a clamped line or a closed stopcock to preventfluid pressure from quickly exceeding a maximum value.

It minimizes the occurrence of nuisance alarms during false "slowocclusions" such as those caused by transient fluctuations such asvascular pressure, head height, or motion of the patient. The systemdoes provide an alarm in the event of true "slow occlusions" which arecaused by pressure slowly increasing to a high level due to a clotted orinfiltrated fluid line. The system of the present invention alsoprovides flexibility in the maximum pressure which may be generatedwithout causing an alarm, and is specifically designed to work with anumber of different pump configurations.

The patient-side occlusion detection system of the present inventionprovides an alarm in a minimal time from the onset of an occlusion. Itaffords a high degree of precision and accuracy which remain constantthroughout the life of the cassette, and it is not be significantlyaffected by other operating components of the system. It requires lowpower to operate, thereby conserving power and extending battery life.The system is of a design which enables it to compete economically withknown competing systems. It accomplishes all the above objects in amanner which retains all of the advantages of ease of use, reliability,durability, and safety of operation, without incurring any relativedisadvantage. The present invention therefore results in a superiormedication infusion system having a number of advantages making thesystem a highly desirable alternative to systems presently available.

Although an exemplary embodiment of the present invention has been shownand described, it will be apparent to those having ordinary skill in theart that a number of changes, modifications, or alterations to theinvention as described herein may be made, none of which depart from thespirit of the present invention. All such changes, modifications, andalterations should therefore be seen as within the scope of the presentinvention.

What is claimed is:
 1. A patient-side occlusion detection system for usein a medication infusion system having a disposable cassette including apump mounted onto a main pump unit, comprising:means for providing anelectrical patient-side pressure signal indicative of patient-side fluidpressure; a differentiator for taking the first difference of saidpatient-side pressure signal to produce a pressure change rate signal; aone-step ahead predictor having as inputs said patient-side pressuresignal and said pressure change rate signal, said one-step aheadpredictor having as an output a predicted future pressure signal; firstmeans for monitoring said one-step ahead predictor whenever saidpressure change rate signal equals or exceeds a first preselected value,said first monitoring means initiating an alarm when said predictedfuture pressure signal exceeds a second preselected value; and secondmeans for monitoring said patient-side pressure signal whenever saidpressure change rate signal is less than said first preselected value,said second monitoring means initiating an alarm when said patient-sidepressure signal exceeds a third preselected value.
 2. A patient-sideocclusion detection system as defined in claim 1, wherein said providingmeans comprises:means for producing an analog electrical patient-sidepressure signal indicative of patient-side fluid pressure; and ananalog-to-digital converter for converting said analog electricalpatient-side pressure signal into said patient-side pressure signal. 3.A patient-side occlusion detection system as defined in claim 2, whereinsaid producing means comprises:a pressure diaphragm in said cassette;and a pressure transducer in said main pump unit for producing saidanalog electrical patient-side pressure signal in response to pressurefrom said pressure diaphragm against said pressure transducer.
 4. Apatient-side occlusion detection system as defined in claim 3, whereinsaid pressure transducer periodically samples said patient-side fluidpressure to produce said analog electrical patient-side pressure signal.5. A patient-side occlusion detection system as defined in claim 4,additionally comprising:an amplifier for amplifying said analogelectrical patient-side pressure signal produced by said pressuretransducer; and a filter for filtering the amplified analog electricalpatient-side pressure signal produced by said amplifier.
 6. Apatient-side occlusion detection system as defined in claim 5, whereinsaid filter is a first order low pass filter.
 7. A patient-sideocclusion detection system as defined in claim 2, wherein saidanalog-to-digital converter comprises:means for periodically samplingsaid analog electrical patient-side pressure signal; and means forquantizing the sampled analog electrical patient-side pressure signalform said sampling means, the output of said quantizing means being saidpatient-side pressure signal, said patient-side pressure signal being adigital signal.
 8. A patient-side occlusion detection system as definedin claim 7, wherein said sampling means comprises a sampler, and saidquantizing means comprises an eight-bit quatizer, the sampling period Tof the sampler being the largest interval maintaining only a preselectedamount of overshoot and udershoot in said predicted future pressuresignal when compared to said patient-side pressure signal.
 9. Apatient-side occlusion detection system as defined in claim 7,additionally comprising:a first order analog filter for filtering saidanalog electrical patient-side pressure signal before it is sampled bysaid sampling means, said analog filter having a time constant of τ₁,said sampling means having a sampling period of T, wherein said firstmeans uses the formula P_(k+1) =(τ₁ +T)*P_(k) +P_(k) to compute a valuefor the predicted future pressure signal P_(k+1), where P_(k) is saidpatient-side pressure signal, P_(k) is said first difference of saidpatient-side pressure signal, and P_(k+1) is said predicted futurepressure signal.
 10. A patient-side occlusion detection system asdefined in claim 1, wherein said first preselected value isapproximately five PSI/sec.
 11. A patient-side occlusion detectionsystem as defined in claim 1, wherein said medication infusion systemmay be configured as any of a plurality of different types of pumps,wherein said second preselected value is approximately six PSI if saidmedication infusion system is configured as a flow controller, orfifteen PSI if said medication infusion system is configured as a deviceother than a flow controller.
 12. A patient-side occlusion detectionsystem as defined in claim 1, wherein said second monitoring meanscomprises:flow controller monitoring means for monitoring saidpatient-side pressure signal whenever said pressure change rate signalis less than said first preselected value and said medication infusionsystem is configured as a flow controller; and infusion pump monitoringmeans for monitoring said patient-side pressure signal whenever saidpressure change rate signal is less than said first preselected valueand said medication infusion system is configured as an infusion pumpother than a flow controller.
 13. A patient-side occlusion detectionsystem as defined in claim 12, wherein said flow controller monitoringmeans compares said patient-side pressure signal to said thirdpreselected value and produces an alarm whenever said patient-sidepressure signal equals or exceeds said third preselected value, saidthird preselected value being between one and one-half and six feet ofwater.
 14. A patient-side occlusion detection system as defined in claim13, additionally comprising:a first order low pass filter for filteringsaid patient-side pressure signal before it is compared to said thirdpreselected value.
 15. A patient-side occlusion detection system asdefined in claim 12, wherein the pump in the disposable cassette is areciprocating pump operating in successive strokes, beginning a pumpingoperation with a first stroke, followed by a second stroke and a thirdstroke, wherein said infusion pump monitoring means comprises:means formonitoring said patient-side pressure signal from the beginning of thesecond stroke of said pump to the beginning of the third stroke of saidpump; means for averaging said monitored patient-side pressure signalfrom the beginning of the second stroke of said pump to produce abaseline pressure; and means for initiating an alarm when saidpatient-side pressure signals exceeds the sum of said baseline pressureplus a fourth preselected value.
 16. A patient-side occlusion detectionsystem as defined in claim 15, wherein said monitoring and averagingsteps are performed each time an infusion regimen is first initiated bysaid medication infusion system, and each time the infusion rate of saidmedication infusion system is changed.
 17. A patient-side occlusiondetection system as defined in claim 15, wherein said medicationinfusion system may be configured as any of a plurality of differenttypes of pumps, wherein said fourth preselected value is approximatelyone PSI if said medication infusion system is configured as a neonatalpump, approximately ten PSI if said medication infusion system isconfigured as an operating room pump, and approximately five PSI if saidmedication infusion system is configured as a general purpose pump. 18.A patient-side occlusion detection system as defined in claim 15,additionally comprising:override means for initiating an alarm wheneversaid patient-side pressure signal is equal to or exceeds a fifthpreselected value, even if said patient-side pressure signal is lessthan said sum of said baseline pressure plus said fourth preselectedvalue.
 19. A patient-side occlusion detection system as defined in claim18, wherein said fifth preselected value is approximately fifteen PSI.20. A patient-side occlusion detection system for use in a medicationinfusion system having a disposable cassette mounted onto a main pumpunit, comprising:means for providing an analog electrical pressuresignal indicative of patient-side fluid pressure; an analog-to-digitalconverter for converting said analog pressure signal into a digitalpressure signal; a differentiator for taking the first difference ofsaid digital pressure signal to produce a digital pressure change ratesignal having a sampling period T; a one-step ahead predictor having asinputs said digital pressure signal and said digital pressure changerate signal, said one-step ahead predictor having as an output apredicted pressure signal for one sampling period T in the future; firstmeans for monitoring said one-step ahead predictor whenever said digitalpressure change rate signal equals or exceeds a first preselected value,said first monitoring means initiating an alarm when said predictedpressure signal exceeds a second preselected value; and second means formonitoring said digital pressure signal whenever said digital pressurechange rate signal is less than said first preselected value, saidsecond monitoring means initiating an alarm when said digital pressuresignal exceeds a third preselected value.
 21. A patient-side occlusiondetection system for use in a medication infusion system having adisposable cassette mounted onto a main pump unit, comprising:means forproviding a digital electrical pressure signal indicative ofpatient-side fluid pressure; means for taking the first difference ofsaid digital pressure signal to produce a digital pressure change ratesignal having a sampling period T; a one-step ahead predictor having asinputs said digital pressure signal and said digital pressure changerate signal, said one-step ahead predictor having as an output apredicted pressure signal for one sampling period T in the future; firstmeans for monitoring said one-step ahead predictor whenever said digitalpressure change rate signal equals or exceeds a first preselected value,said first monitoring means initiating an alarm when said predictedpressure signal exceeds a second preselected value; and second means formonitoring said digital pressure signal whenever said digital pressurechange rate signal is less than said first preselected value, saidsecond monitoring means calculating a baseline pressure shortly afterinfusion is begun, said second monitoring means initiating an alarm whensaid digital pressure signal exceeds the sum of said baseline pressureplus a third preselected value.
 22. A method of detecting a patient-sideocclusion in a medication infusion system having a disposable cassettemounted onto a main pump unit, comprising:providing an electricalpatient-side pressure signal indicative of patient-side fluid pressure;taking the first difference of said patient-side pressure signal toproduce a pressure change rate signal having a sampling period T; usinga one-step ahead predictor to calculate a predicted pressure signal forone sampling period T in the future, said one-step ahead predictorhaving as inputs said patient-side pressure signal and said pressurechange rate signal; monitoring said one-step ahead predictor wheneversaid pressure change rate signal equals or exceeds a first preselectedvalue, said first monitoring means initiating an alarm when saidpredicted pressure signal exceeds a second preselected value; andmonitoring said patient-side pressure signal whenever said pressurechange rate signal is less than said first preselected value, saidsecond monitoring means initiating an alarm when said patient-sidepressure signal exceeds a third preselected value.